Paju, South Korea (CNN) North Korea outlined an ultimatum Friday to its southern neighbor: Stop the "provocations" and "psychological warfare" or pay the price.

"If South Korea does not respond to our ultimatum," North Korean U.N. ambassador An Myong Hun told reporters, "our military counteraction will be inevitable and that counteraction will be very strong."

North Korea's regime, known for being both thin-skinned and fond of saber rattling , has made plenty of threats before. In fact, articulating derogatory and intimidating words about South Korea and the United States has been more the norm than not for years.

What makes this case different, though, is that two South Korean soldiers have been seriously wounded (by landmines August 4 in the Demilitarized Zone) and that there's been firing back-and-forth since then. An said Friday that "all the (North Korean) frontline large combined units (have) entered into a wartime state ... fully armed to launch any surprise operations and finish their preparations for action."

Specifically, this threat is tied to cross-border propaganda loudspeakers that South Korea resumed using last week for the first time in a decade. Pyongyang is demanding they be turned off by Saturday evening.

"The situation of the country is now inching closer to the brink of war," Ji Jae Ryong, North Korean ambassador to China, told journalists in Beijing on Friday.

U.S., South Korea exercises resume

South Korean Defense Minister Han Min-koo accused North Korea of pushing the tensions "to the utmost level."

"North Korea's offensive action is a despicable crime that breaks a ceasefire agreement and the non-aggression treaty between North and South," Han said Friday in an address broadcast on South Korean television.

"If North Korea continues on provoking, our military -- as we have already warned -- will respond sternly, and end the evil provocations of North Korea," he said, adding the country is working closely with the United States.

As the verbal sniping continued, the South's President, Park Geun-hye, visited troops at a base south of Seoul, receiving a briefing from military officials on the latest situation, her office said.

One ongoing point of contention is South Korea's joint military exercises with the United States -- a regular training event that An contends aims to "occupy Pyongyang."

Those exercises were suspended Thursday amid the war of words, U.S. Assistant Secretary of Defense David Shear told reporters. But they're now back on.

"We suspended part of the exercise temporarily in order to allow our side to coordinate with the ROK (Republic of Korea) side on the subject of the exchange fire across the DMZ," Shear said "And the exercise is being conducted now according to plan."

North Korea calls broadcasts 'an open act of war'

Tensions on the Korean Peninsula have been escalating since the two South Korean soldiers were wounded early this month. South Korea and the U.S.-led U.N. Command in Korea concluded North Korea planted the mines on a patrol route in the southern part of the zone.

North Korea has denied responsibility and refused South Korean demands for an apology.

"It is a bad habit (for) South Korea to groundlessly link whatever events occur in South Korea with the DPRK," An said, with the DPRK equating to his country. "They seek sinister purposes whenever they orchestrate ridiculous plots."

Seoul has since resumed its cross-border propaganda broadcasts, which North Korea called "an open act of war" and spurred it to threaten to blow up the speakers.

Photos: Kim Jong Un and North Korea's military Photos: Kim Jong Un and North Korea's military North Korean leader Kim Jong Un meets with North Korea's first female fighter jet pilots in this undated photo released by the country's state media on Monday, June 22. He called the women "heroes of Korea" and "flowers of the sky." Hide Caption 1 of 55 Photos: Kim Jong Un and North Korea's military Kim stands on the snow-covered top of Mount Paektu in North Korea in a photo taken by North Korean newspaper Rodong Sinmun on April 18 and released the next day by South Korean news agency Yonhap. Kim scaled the country's highest mountain, North Korean state-run media reported, arriving at the summit to tell soldiers that the hike provides mental energy more powerful than nuclear weapons. Hide Caption 2 of 55 Photos: Kim Jong Un and North Korea's military Kim Jong Un, center, poses with soldiers on the snow-covered top of Mount Paektu in an April 18 photo released by South Korean news agency Yonhap. Hide Caption 3 of 55 Photos: Kim Jong Un and North Korea's military Kim visits the Kumsusan Palace of the Sun in Pyongyang, North Korea, on April 15 to celebrate the 103rd birth anniversary of his grandfather, North Korean founder Kim Il Sung. Hide Caption 4 of 55 Photos: Kim Jong Un and North Korea's military Kim inspects a drill for seizing an island at an undisclosed location in North Korea in an undated picture released by North Korea's official Korean Central News Agency on February 21. Hide Caption 5 of 55 Photos: Kim Jong Un and North Korea's military Kim speaks during a meeting of the Political Bureau of the Central Committee of the Workers' Party of Korea in Pyongyang, North Korea, in this photo released February 19 by the state-run Korean Central News Agency. Hide Caption 6 of 55 Photos: Kim Jong Un and North Korea's military A picture released by the North Korean Central News Agency shows North Korean leader Kim Jong Un appearing without his cane at an event with military commanders in Pyongyang on Tuesday, November 4. Kim, who recently disappeared from public view for about six weeks, had a cyst removed from his right ankle, a lawmaker told CNN. Hide Caption 7 of 55 Photos: Kim Jong Un and North Korea's military Kim is seen walking with a cane in this image released Thursday, October 30, by the state-run Korean Central News Agency. Hide Caption 8 of 55 Photos: Kim Jong Un and North Korea's military Kim sits in the pilot's seat of a fighter jet during the inspection. Hide Caption 9 of 55 Photos: Kim Jong Un and North Korea's military This undated photo, released Tuesday, October 14, by the KCNA, shows Kim inspecting a housing complex in Pyongyang, North Korea. International speculation about Kim went into overdrive after he failed to attend events on Friday, October 10, the 65th anniversary of the Workers' Party. He hadn't been seen in public since he reportedly attended a concert with his wife on September 3. Hide Caption 10 of 55 Photos: Kim Jong Un and North Korea's military A picture released by the KCNA shows Kim and his wife watching a performance by the Moranbong Band on Wednesday, September 3, in Pyongyang. Hide Caption 11 of 55 Photos: Kim Jong Un and North Korea's military Kim tours a front-line military unit in this image released Wednesday, July 16, by the KCNA. Hide Caption 12 of 55 Photos: Kim Jong Un and North Korea's military Kim poses for a photo as he oversees a tactical rocket-firing drill in June. Hide Caption 13 of 55 Photos: Kim Jong Un and North Korea's military Kim watches a tactical rocket-firing drill in June. Hide Caption 14 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier patrols the bank of the Yalu River, which separates the North Korean town of Sinuiju from the Chinese border town of Dandong, on Saturday, April 26. Hide Caption 15 of 55 Photos: Kim Jong Un and North Korea's military In this photo released Thursday, April 24, by the Korean Central News Agency, Kim smiles with female soldiers after inspecting a rocket-launching drill at an undisclosed location. Hide Caption 16 of 55 Photos: Kim Jong Un and North Korea's military A picture released Tuesday, March 18, by the KCNA shows Kim attending a shooting practice at a military academy in Pyongyang. Hide Caption 17 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier uses binoculars on Thursday, February 6, to look at South Korea from the border village of Panmunjom, which has separated the two Koreas since the Korean War. Hide Caption 18 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier kicks a pole along the banks of the Yalu River on Tuesday, February 4. Hide Caption 19 of 55 Photos: Kim Jong Un and North Korea's military A photo released by the KCNA on Thursday, January 23, shows the North Korean leader inspecting an army unit during a winter drill. Hide Caption 20 of 55 Photos: Kim Jong Un and North Korea's military Kim inspects the command of an army unit in this undated photo released Sunday, January 12, by the KCNA. Hide Caption 21 of 55 Photos: Kim Jong Un and North Korea's military Kim visits an army unit in this undated photo. Hide Caption 22 of 55 Photos: Kim Jong Un and North Korea's military Kim inspects a military factory in this undated picture released by the KCNA in May 2013. Hide Caption 23 of 55 Photos: Kim Jong Un and North Korea's military Kim visits the Ministry of People's Security in 2013 as part of the country's May Day celebrations. Hide Caption 24 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier, near Sinuiju, gestures to stop photographers from taking photos in April 2013. Hide Caption 25 of 55 Photos: Kim Jong Un and North Korea's military North Korean soldiers patrol near the Yalu River in April 2013. Hide Caption 26 of 55 Photos: Kim Jong Un and North Korea's military Kim is briefed by his generals in this undated photo. On the wall is a map titled "Plan for the strategic forces to target mainland U.S." Hide Caption 27 of 55 Photos: Kim Jong Un and North Korea's military Kim works during a briefing in this undated photo. Hide Caption 28 of 55 Photos: Kim Jong Un and North Korea's military In this KCNA photo, Kim inspects naval drills at an undisclosed location on North Korea's east coast in March 2013. Hide Caption 29 of 55 Photos: Kim Jong Un and North Korea's military Kim, with North Korean soldiers, makes his way to an observation post in March 2013. Hide Caption 30 of 55 Photos: Kim Jong Un and North Korea's military Kim uses a pair of binoculars to look south from the Jangjae Islet Defense Detachment, near South Korea's Taeyonphyong Island, in March 2013. Hide Caption 31 of 55 Photos: Kim Jong Un and North Korea's military Kim is greeted by a soldier's family as he inspects the Jangjae Islet Defense Detachment in March 2013. Hide Caption 32 of 55 Photos: Kim Jong Un and North Korea's military Kim is surrounded by soldiers during a visit to the Mu Islet Hero Defense Detachment, also near Taeyonphyong Island, in March 2013. Hide Caption 33 of 55 Photos: Kim Jong Un and North Korea's military Kim arrives at Jangjae Islet by boat to meet with soldiers of the Jangjae Islet Defense Detachment in March 2013. Hide Caption 34 of 55 Photos: Kim Jong Un and North Korea's military Soldiers in the North Korean army train at an undisclosed location in March 2013. Hide Caption 35 of 55 Photos: Kim Jong Un and North Korea's military In a photo released by the official North Korean news agency in December 2012, Kim celebrates a rocket's launch with staff from the satellite control center in Pyongyang. Hide Caption 36 of 55 Photos: Kim Jong Un and North Korea's military Kim, center, poses in this undated picture released by North Korea's official news agency in November 2012. Hide Caption 37 of 55 Photos: Kim Jong Un and North Korea's military Kim visits the Rungna People's Pleasure Ground, under construction in Pyongyang, in a photo released in July 2012 by the KCNA. Hide Caption 38 of 55 Photos: Kim Jong Un and North Korea's military A crowd watches as statues of North Korean founder Kim Il Sung and his son Kim Jong Il are unveiled during a ceremony in Pyongyang in April 2012. Hide Caption 39 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier stands guard in front of an UNHA III rocket at the Tangachai-ri Space Center in April 2012. Hide Caption 40 of 55 Photos: Kim Jong Un and North Korea's military In April 2012, Pyongyang launched a long-range rocket that broke apart and fell into the sea. Here, the UNHA III rocket is pictured on its launch pad in Tang Chung Ri, North Korea. Hide Caption 41 of 55 Photos: Kim Jong Un and North Korea's military – A closer look at the UNHA III rocket on its launch pad in Tang Chung Ri, North Korea. Hide Caption 42 of 55 Photos: Kim Jong Un and North Korea's military A military vehicle participates in a parade in Pyongyang in April 2012. Hide Caption 43 of 55 Photos: Kim Jong Un and North Korea's military North Korean soldiers relax at the end of an official ceremony attended by leader Kim Jong Un at a stadium in Pyongyang in April 2012. Hide Caption 44 of 55 Photos: Kim Jong Un and North Korea's military Kim Jong Un applauds as he watches a military parade in Pyongyang in April 2012. Hide Caption 45 of 55 Photos: Kim Jong Un and North Korea's military A North Korean soldier stands on a balcony in Pyongyang in April 2012. Hide Caption 46 of 55 Photos: Kim Jong Un and North Korea's military North Korean soldiers march during a military parade in Pyongyang in April 2012. Hide Caption 47 of 55 Photos: Kim Jong Un and North Korea's military Soldiers board a bus outside a theater in Pyongyang in April 2012. Hide Caption 48 of 55 Photos: Kim Jong Un and North Korea's military North Korean performers sit below a screen showing images of leader Kim Jong Un in Pyongyang in April 2012. Hide Caption 49 of 55 Photos: Kim Jong Un and North Korea's military North Korean soldiers salute during a military parade in Pyongyang in April 2012. Hide Caption 50 of 55 Photos: Kim Jong Un and North Korea's military North Korean soldiers listen to a speech during an official ceremony attended by leader Kim Jong Un at a stadium in Pyongyang in April 2012. Hide Caption 51 of 55 Photos: Kim Jong Un and North Korea's military Members of a North Korean military band gather following an official ceremony at the Kim Il Sung stadium in Pyongyang in April 2012. Hide Caption 52 of 55 Photos: Kim Jong Un and North Korea's military North Korean military personnel watch a performance in Pyongyang in April 2012. Hide Caption 53 of 55 Photos: Kim Jong Un and North Korea's military A North Korean controller is seen along the railway line between the Pyongyang and North Pyongan provinces in April 2012. Hide Caption 54 of 55 Photos: Kim Jong Un and North Korea's military A North Korean military honor guard stands at attention at Pyongyang's airport in May 2001. Hide Caption 55 of 55

On Thursday, South Korean officials said the North fired artillery shells over the Demilitarized Zone that separates the two countries. A U.S. official told CNN that North Korea was believed to be targeting a loudspeaker position.

The South fired back several dozen shells of its own, according to the Defense Ministry.

No casualties were reported by either side.

Amid the tensions, South Korean officials said some residents of the area targeted by North Korea on Thursday had to be evacuated, although many have since returned.

History of disputes

It's not the first time that the two sides have briefly traded blows in recent years. They notably exchanged artillery fire over their disputed maritime border in 2010 and machine-gun fire over land in October

But Thursday's clash was unusual because of the type of weapons used around the Demilitarized Zone, said Alison Evans, a senior analyst at IHS Country Risk.

"Cross-border attacks have mainly involved small-arms fire or, as in October 2014, anti-aircraft heavy machine guns," she said. "In contrast, there have been frequent exchanges of artillery and rocket fire across the Northern Limit Line (NLL), the de facto maritime border."

Amid the heightened tensions, North Korea's connection to the global Internet went down twice Friday, according to Dyn Research, a U.S-based private Internet-monitoring service. North Korea's Internet access last went down August 10 for 4 ½ hours, according to Dyn Research. The cause of the disruption was not immediately clear.

Is situation likely to escalate?

The question now is whether the situation will escalate further.

North Korea has used similarly alarming language in previous periods of high tension

In 2013, the country announced it had entered "a state of war" with South Korea. That situation didn't result in military action, although North Korea did temporarily shut down the two countries' joint industrial zone, which lies on its side of the border.

During that period, North Korea kept up a barrage of bombastic threats against the United States, South Korea and Japan. But at the same time, it continued accepting tourists and hosting international athletes in Pyongyang for a marathon.

South Korea said Friday that it was limiting the number of its citizens entering the joint industrial zone, but the complex was still operating. There are currently 83 South Koreans in Pyongyang attending a youth soccer event, including players and coaches, according to the South Korean Unification Ministry.

Jamie Metzl, an Asia expert for the Atlantic Council in New York, said he thought it was unlikely that the current crisis would escalate further.

"North Korea has more to gain from conflict theater than from a conflict that would quickly expose its fundamental weakness," he said, suggesting leaders in Pyongyang might be trying to "make trouble because they feel ignored by the international community and feel they have something to gain negotiating their way out of a mini-crisis."

But other analysts said the situation could still continue to deteriorate.

The shelling Thursday "raises questions frankly about Kim Jong Un's style of making tension, provocations, escalation -- and whether he knows how to control escalation," said Michael Green, an Asia specialist at the Center for Strategic and International Studies.

U.S., China, urge calm

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A spokeswoman for China's Foreign Ministry said Friday that the country is "paying great attention to the situation" and is "willing to work with all parties toward the peace and stability of the peninsula."

"We urge relevant parties to remain calm and restrained, use meetings and dialogue to properly handle the current situation, and stop any action that could escalate the tensions," spokeswoman Hua Chunying said.

U.N. Secretary-General Ban Ki-moon is "deeply concerned" about the situation, spokesman Eri Kaneko said.

The United States, which has roughly 28,000 troops stationed in South Korea, said it, too, is closely monitoring the situation.

"As we've said before, these kinds of provocative actions only heighten tensions," State Department spokesman John Kirby said Thursday, referring to the North Korean shelling. "And we call on Pyongyang to refrain from actions and rhetoric that threaten regional peace and security."

He said that Washington and Seoul are coordinating closely and that the United States "remains steadfast in its commitment to the defense, the security of the peninsula, to our alliance with South Korea."