Seoul, South Korea (CNN) South Korea strengthened the deployment of a controversial US-made missile defense system and launched a huge show of military might on Monday in response to North Korea's test of what it claimed to be a hydrogen bomb.

Seoul said the North appeared to be preparing to launch more missiles after Sunday's test rocked the region. South Korea conducted a series of live-fire drills and said the US was preparing to bolster its military presence.

Russia warned that it would consider ramping up its military assets in response, and China warned that the deployment of the missile defense system,THAAD, risked escalating the already tense situation.

The deepening crisis has caused frayed relations on both sides. North Korea's continued belligerence was a blow to China, which has failed to keep its ally in check despite persistent warnings. China said Monday it had made a "stern representation" to North Korea over the test.

Meanwhile Donald Trump, the US president, opened up a rift with South Korea, saying it risked "appeasement" of Pyongyang.

Latest developments:

-- Briefing parliament, South Korean military officials said there were ongoing signs that Pyongyang was preparing to test another Intercontinental ballistic missile (ICBM).

-- Seoul said it would activate four Terminal High Altitude Area Defense (THAAD) launch pads and said the US was considering the deployment of an aircraft carrier and more bombers.

-- Russian Deputy Foreign Minister Sergey Ryabkov said Moscow could increase its missile presence in the Pacific in response to the deployment of the US missile defense system.

-- South Korea conducted a series of military drills, including a simulation of an attack on the North's nuclear-testing site. More live-fire tests would follow, it said.

-- At an emergency session of the United Nations Security Council in New York, US ambassador Nikki Haley said North Korean leader Kim Jong Un was "begging for war."

-- US defense secretary, James Mattis, said any threat from North Korea to the US would be met with a "massive military response."

South Korea's response

Seoul responded to North Korea's nuclear test with a show of military might that was intended to demonstrate its willingness to "wipe out" the regime of Kim Jong Un, South Korea's Defense Ministry said.

South Korea's army and air force carried out a joint drill that involved multiple F-15K fighter jets and surface-to-surface ballistic missiles. They hit targets off the country's east coast to simulate a strike on North Korea's nuclear test site, according to a statement from the South Korean Joint Chiefs of Staff.

In this photo provided by South Korea Defense Ministry, South Korea's Hyunmoo II ballistic missile is fired during an exercise at an undisclosed location on Monday.

At a Defense Ministry press conference, Major General Jang Kyung Soo, said South Korea had detected "continuous signs" that North Korea was preparing another ICBM test. He said the North could launch the missiles ahead of September 9, the anniversary of the day North Korea was founded, in a show of celebration at home and defiance to the US.

He said South Korea plans to carry out another missile drill to show its "strong will and ability to respond."

On Sunday Pyongyang claimed it has the ability to place a miniaturized nuclear weapon on an ICBM. If confirmed, it would be a significant advance for its weapons program, achieved far sooner than experts had predicted.

Rift with Washington

South Korea said President Moon Jae-in would speak with President Trump on the telephone later Monday. They have not spoken since Sunday's test, though US and South Korean military advisers have been in touch. Instead, Trump warned South Korea in a Twitter message Sunday that "talk of appeasement" would not work.

It was unclear what prompted the comment. In the past, President Moon has advocated dialogue with Pyongyang. Moon's office responded by reiterating the government would "pursue the denuclearization of the Korean Peninsula through peace with our allies."

Adam Schiff, the top Democrat on the US House of Representatives Intelligence Committee, cautioned against criticizing South Korea.

"I'm sure that Pyongyang enjoys seeing us fight with our own ally in the region," Schiff said. "We need to be working hand in hand with South Korea and with Japan... why we would want to show divisions with South Korea makes no sense at all."

China embarrassed

Pyongyang's actions appear, in part, designed to test the limits of China's support. Experts say its latest nuclear test could have been timed to coincide an international economic summit currently being hosted in Beijing.

North Korea has timed missile tests this year to coincide with other important Chinese events, including a missile test during a summit in May on China's "Belt and Road" regional economic initiative.

Geng Shuang, a spokesperson for the Chinese Foreign Ministry said Bejing had "launched stern representation" to North Korea over its nuclear test. In a regular press briefing Monday, Geng said the test was "wrong" and "against the will of the international community and will meet with China's disapproval."

He said China opposed North Korea's missile development program and said it wanted to return to six-party talks as soon as possible.

Responding to a question about the deployment of more US military assets in the region, Geng said China hoped all sides would "work to ease the tension instead of escalating the tension."

Trump criticized China in his series of tweets Sunday, saying North Korea's actions were a "great threat and embarrassment to China, which is trying to help but with little success."

Trump also said that the US was considering cutting off all trade with any country that carried out business with North Korea. That would include China, which provides an economic lifeline to North Korea. China is the largest US trading partner in terms of goods, and a trade war between the two nations could be devastating.

North Korea's 2015 imports Source: Observatory of Economic Complexity

Geng said it was "unacceptable" and "not fair" to be sanctioned for trading with North Korea when it is working hard to "peacefully resolve" tensions. China was "committed to resolving this issue through dialogue and consultation," he said.

International response

On Monday, US Ambassador to the United Nations Nikki Haley said that North Korean leader Kim Jong Un was "begging for war" and urged the UN Security Council to adopt the strongest sanctions measures possible to stop Pyongyang's nuclear program.

"War is never something the Unites States wants - we don't want it now but our countries patience is not unlimited - we will defend our allies and our territory," she said at an emergency session of the UN Security Council.

US and its allies are looking to push through a new package of sanctions, including measures to restrict oil shipments to North Korea, US officials said. Most of North Korea's oil comes from China, and the US believes that stopping these shipments would place severe pressure on the North Korean regime.

Haley said North Korea's sixth nuclear test was a clear sign that "the time for half measures" from the UN had to end.

"Enough is enough," Haley said. "We have taken an incremental approach, and despite the best of intentions, it has not worked."

The UN passed its latest set of sanctions -- some of the most stringent to date -- in early August. The Trump administration has started punishing companies for doing business with North Korea -- so-called "secondary sanctions."