Tensions rising as North Korea carries out new artillery excercises

Nuclear-armed North Korea on Tuesday marked a military anniversary with a massive conventional firing drill, Seoul said, as a U.S. guided-missile submarine docked in South Korea amid tensions over Pyongyang's weapons ambitions.

Experts fear Pyongyang could be planning more tests - it has marked some key anniversaries in the past with nuclear tests or missile launches.

A U.S. submarine has arrived in South Korea, amid worries of another North Korean missile or nuclear test.

Xi told Trump China "hopes that all relevant sides exercise restraint, and avoid doing anything to worsen the tense situation", China's foreign ministry said in a statement.

Military exercises such as the one undertaken by North Korea are not unprecedented and it was always likely there would have been a show of military force on Armed Forces Day.

It highlights Chinese fears that tensions between the United States and North Korea could erupt into conflict.

He told the gathering: "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 USA imperialists and their vassal forces for aggression".

Kim did not attend. It was not known how he is marking Tuesday's anniversary.

North Korea has reportedly conducted a huge live-fire exercise to mark the foundation of its military.

North Korean military personnel salute toward the statues of Kim Il-sung and Kim Jong-il at Mansudae Hill in Pyongyang on April 25, 2017.

Envoys on North Korean affairs from the U.S., Japan and South Korea agreed on Tuesday to keep pressuring Kim's regime to give up its nuclear program, including through sanctions and cooperation with China.

The USS Michigan, a nuclear powered submarine, also arrived in the South Korean port city of Busan on Tuesday.

A South Korean government official said that "there are indications that this is a large-scale exercise" in the area of Wonsan.

The supercarrier leading the strike group, the USS Carl Vinson, is expected to reach Korean waters sometime before the end of April.

North Korea condemned Trump for planning the briefing, along with the State Department's move to hold a meeting of UN Security Council foreign ministers on Friday. North Korea's growing nuclear and missile threat is perhaps the most serious security challenge confronting U.S. President Donald Trump.

Meanwhile, top envoys for North Korea policy from the US, South Korea, and Japan have met to discuss Pyongyang.

Trump spoke by phone with both the Japanese and Chinese leaders Monday.

The port call by the USS Michigan came as a USA aircraft carrier strike group steams for Korean waters and as the top nuclear envoys from South Korea, Japan and the United States met in Tokyo to discuss the North's refusal to give up its nuclear program.

In Washington, the Trump administration invited the entire 100-member Senate for a briefing Wednesday on the escalating crisis.

"The status quo in North Korea is also unacceptable", Trump told a meeting with the 15 UN Security Council ambassadors, including China and Russian Federation, at the White House.

The White House said Trump and Xi "reaffirmed the urgency of the threat posed by North Korea's missile and nuclear programmes, and committed to strengthen coordination in achieving the denuclearisation of the Korean peninsula".

South Korea says a US nuclear-powered submarine has docked in the southern port of Busan, but it isn't expected to participate in joint naval exercises with South Korea.

Kim said they discussed ways to get more cooperation from China and Russian Federation, which they agreed is crucial to applying effective pressure on North Korea to abandon its nuclear weapons program.

In a separate meeting slated for Wednesday, high-ranking military officials will brief senators on North Korea, the Pentagon said.