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PYONGYANG, North Korea — South Korea's military said Tuesday that North Korea held major live-fire drills in an area around its eastern coastal town of Wonsan as it marked the anniversary of the founding of its military.

The exercise took place as a U.S. guided-missile submarine arrived in South Korea and envoys from the United States, Japan and South Korea met in Tokyo to discuss the growing threat posed by North Korea's nuclear weapons and missiles program.

Though experts thought a nuclear test or ballistic missile launch might happen, the morning came and went without either.

North Korean General Warns of Pre-emptive Strike

Crowds in Pyongyang, the North Korean capital, laid flowers and paid respects at giant statues of the country's former leaders Kim Il Sung and Kim Jong Il, one day after the minister of defense reiterated that the North is ready to use pre-emptive strikes or any measures it deems necessary to defend itself against the "U.S. imperialists."

"The situation prevailing on the Korean Peninsula is so tense that a nuclear war may break out due to the frantic war drills of the U.S. imperialists and their vassal forces for aggression," Gen. Pak Yong Sik told a "national meeting" of thousands of senior military and civilian officials.

South Korea's Joint Chiefs of Staff said it is closely watching North Korean military action in the Wonsan city area, where it said the drills were being held. South Korea's Yonhap news agency earlier said that the exercise involved 300 to 400 artillery pieces, but an official from Seoul's Defense Ministry couldn't confirm such details.

The streets of Pyongyang were quiet. Flower-laying and bowing at statues and portraits of the leaders is a regular routine on major anniversaries. People also gathered in open spaces to take part in organized dancing, another common way to mark holidays.

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"Our great leaders founded and wisely led our revolutionary army, and just like that, now our respected Marshal Kim Jong Un is leading wisely, so even though the situation is tense, we are celebrating the day," said Choe Un Byol, who had come with his family to the bronze statues of the former leaders.

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North Korea often also marks significant dates by displaying its military capability. Pyongyang launched a missile one day after the 105th birthday of late founder Kim Il Sung on April 15.

Recent U.S. commercial satellite images indicate increased activity around North Korea's nuclear test site, and third-generation dictator Kim has said the country's preparation for an ICBM launch is in its "final stage."

U.S. Navy Gathers Off Koreas

The USS Michigan, a nuclear-powered submarine, arrived at the South Korean port of Busan in what was described as a routine visit to rest the crew and load supplies. Cmdr. Jang Wook from South Korean navy public affairs said there was no plan for a drill.

The submarine's arrival comes as the USS Carl Vinson aircraft carrier heads toward the Korean Peninsula for a joint exercise with South Korea around the weekend.

Related: VP Pence on North Korea: All Option Are On The Table

Despite the buildup, President Donald Trump has reportedly settled on a strategy that emphasizes increased pressure on North Korea with the help of China, the North's only major ally, instead of military options or trying to overthrow North Korea's government.

Washington's Words

Trump told ambassadors from U.N. Security Council member countries that they must be prepared to impose additional and stronger sanctions on North Korea.

"This is a real threat to the world, whether we want to talk about it or not," Trump said at a White House meeting Monday. "North Korea is a big world problem, and it's a problem we have to finally solve. People have put blindfolds on for decades, and now it's time to solve the problem."

Nikki Haley, Trump's U.N. ambassador, said the United States is not looking for a fight with Kim and would not attack North Korea "unless he gives us reason to do something." She praised China's increased pressure on North Korea.

Asked about the threshold for U.S. action, Haley told American broadcaster NBC that "if you see him attack a military base, if you see some sort of intercontinental ballistic missile, then obviously we're going to do that."

But asked what if North Korea tests an intercontinental missile or nuclear device, she said: "I think then the president steps in and decides what's going to happen."

Diplomats Meet in Tokyo

The United States, Japan and South Korea agreed Tuesday to put maximum pressure on North Korea, the South's envoy for North Korea said after meeting his American and Japanese counterparts in Tokyo.

Related: China Calls for Restraint on North Korea as USS Carl Vinson Arrives

"We agreed to warn North Korea to stop any additional strategic provocation and take intolerably strong punitive measures against Pyongyang if it goes ahead with such provocations," Kim Hong-kyun told reporters following his meeting with Joseph Yun of the U.S. and Japan's Kenji Kanasugi.

Kim said they discussed ways to get more cooperation from China and Russia, which they agreed is crucial to applying effective pressure on North Korea to abandon its nuclear weapons program. He said they also recognized China's recent steps toward that goal.

Japan's Foreign Ministry announced that China's envoy for North Korea, Wu Dawei, was arriving in Tokyo on Tuesday for talks with Kanasugi that may take place later this week.