Tensions boiled over as North Korea indicated that it was prepared for an "invasion" from the US and ready to hit back with a nuclear attack. US President Donald Trump responded by saying that North Korea was "asking for trouble".
Temperatures have risen swiftly since the US decided to deploy warships to the Korean peninsula.
A US naval strike force - led by the nuclear-powered aircraft carrier USS Carl Vinson - cancelled a planned trip to Australia and instead set off for the Korean peninsula from Singapore last Saturday.
Military chief Hwang Pyong So, viewed as the No. 2 man in North Korea, said on Monday the country will "mount a pre-emptive nu- clear attack on South Korea and the United States and wipe them out without traces if they attempt to launch a war of aggression".
A North Korean Foreign Ministry spokesman said of the deployment: "This goes to prove that the US' reckless moves for invading the DPRK have reached a serious phase. The DPRK is ready to react to any mode of war desired by the US." The DPRK, or the Democratic People's Republic of Korea, is the country's official name.
The US warships are expected to reach the Korean peninsula around April 25, Japan's Asahi Shimbun reported.
The developments have raised fears of military escalation, with talk that Pyongyang may conduct a nuclear test to mark the 105th birthday of its founding leader Kim Il Sung on Saturday. The country often marks key anniversaries with nuclear or missile tests.
North Korea, which is working on nuclear-tipped missiles that can hit the US, has become a major headache for the Trump administration, which has previously said that all options are on the table, including military strikes.
Yesterday, Mr Trump, who has urged China to rein in its neighbour, said in a tweet: "North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them!"
He said he told Chinese President Xi Jinping, who he met for the first time in Florida last week, that "a trade deal with the US will be far better for them if they solve the North Korean problem".
China yesterday repeated calls for restraint. Ms Hua Chunying, spokesman for China's Foreign Ministry, said she was unaware of a South Korean media report stating that 150,000 Chinese troops had been deployed to the North Korean border after US air strikes on Syria last week.
In South Korea, Acting President Hwang Kyo Ahn has asked the military to step up monitoring and communication with the US, as Pyong- yang may launch "greater provocations" such as a nuclear test to mark various anniversaries.
Talk of war has spread on South Korean social media, but the country's Foreign Ministry spokesman Cho June Hyuck said the speculation of imminent war is "groundless", as the US will not seek military options against Pyongyang without coordination with Seoul.
Mr Moon Jae In, the front runner in the May 9 presidential election in South Korea, told local media that the South must negotiate with North Korean leader Kim Jong Un to resolve the nuclear issue.
Joint talks between six nations - China, Japan, North Korea, South Korea, the United States and Russia, which yesterday expressed worries about "what Washington has in mind for North Korea" - collapsed in 2009.
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