Tensions have spiked as President Donald Trump's administration has hinted it will take a tougher line against North Korea, which has conducted two nuclear tests and test-fired almost 30 missiles since past year.
North Korea issued a forceful response to the deployment of a United States naval strike group to the region, saying it would counter "reckless acts of aggression" with "whatever methods the USA wants to take".
The Trump administration has been strongly pressuring China to rein in its neighbor, but while China appears to have cut certain trade ties, Beijing has yet to provide any concrete commitments.
China has agreed to "strong" new measures to punish North Korea if it carries out a nuclear test, Seoul said on Monday after the U.S. signalled it may act to shut down Pyongyang's weapons program.
The strike group - which includes the Nimitz-class aircraft supercarrier USS Carl Vinson - cancelled a planned trip to Australia this weekend to head to the Korean peninsula in a show of force.
After the USA redeployed ships heading toward Australia to the Korean Peninsula, North Korea reacted angrily. North Korea often also marks important anniversaries with tests of its nuclear or missile capabilities.
A spokesman of the North Korean Foreign Ministry said through the state-run Korean Central News Agency (KCNA) that it will hold the United States "wholly accountable for the catastrophic consequences entailed by its outrageous actions", adding that Pyongyang is "ready to react to any mode of war".
"The DPRK is ready to react to any mode of war desired by the USA", he said.
NORTH KOREA denounced Washington's deployment of a naval strike group to the Korean Peninsula on Tuesday, warning it was ready for war in a further escalation of tensions in the region.
Tillerson also shared concerns about how close North Korea is to developing nuclear weapons that could be put on missiles that could reach the U.S.
This means that North Korea is willing to take out its big guns if the situation asks for them.
U.S. President Donald Trump, who demonstrated his resolve to use military force if needed with the Syria operation, and his Chinese counterpart Xi Jinping failed to produce a significant breakthrough in ways to resolve the North Korea problem in their summit talks last week.
South Korea's Unification Minister Hong Yong-Pyo said that the repercussions of a potential military response were worrying.
White House officials have signaled that they will consider action against North Korea.
A top North Korea official stated Pyongyang intends to "relentlessly strengthen" the country's nuclear weapons during a meeting of North Korea's parliament commemorating Kim Jong Un's fifth year of rule.
The Supreme People's Assembly, nominally the highest organ of government, usually meets once or twice a year.
April 15 marks the 105th anniversary of the birth of North Korea's first leader, Kim Il Sung.
On Tuesday, a fleet of North Korean cargo ships headed home, mostly fully laden, after China ordered its trading companies to return coal, sources with direct knowledge of the trade said. The Chinese foreign ministry, though, is attempting to calm everyone down, even as rumors swirl of a massive mobilization of troops to the North Korean border.