SEOUL (Reuters) - North Korea conducted a big live-fire exercise on Tuesday to mark the foundation of its military and a U.S. submarine docked in South Korea in a show of force amid growing concern over the North's nuclear and missile programmes.
The port call by the USS Michigan, which is designed to carry ballistic missiles and cruise missiles, came as a U.S. aircraft carrier strike group steamed towards Korean waters in an effort to deter North Korea from a sixth nuclear test or more missile launches in defiance of U.N. sanctions.
Instead of a nuclear blast or a big missile test, North Korea marked Tuesday's 85th anniversary of the founding of its military by deploying a large number of long-range artillery units on its east coast for a live-fire drill, South Korea's military said.
South Korea's Office of Joint Chiefs of Staff said it was monitoring the situation and "firmly maintaining readiness".
South Korea's navy said it was conducting its own live-fire exercise with U.S. destroyers in waters west of the Korean peninsula and would soon join the approaching U.S. carrier group.
North Korea was defiant, saying its military was prepared "to bring to closure the history of U.S. scheming and nuclear blackmail".
"There is no limit to the strike power of the People's Army armed with our style of cutting-edge military equipment, including various precision and miniaturised nuclear weapons and submarine-launched ballistic missiles," the official Rodong Sinmun newspaper said in a front-page editorial.
North Korea's growing nuclear and missile threat is perhaps the most serious security challenge confronting U.S. President Donald Trump. He has vowed to prevent North Korea from being able to hit the United States with a nuclear missile and has said all options are on the table, including a military strike.
Trump sent the USS Carl Vinson aircraft carrier strike group for exercises off the Korean peninsula as a warning to Pyongyang, but U.S. officials say sanctions, not military strikes, are the preferred option.
On Monday, Trump called North Korea a global threat and "a problem that we have to finally solve" and said the U.N. Security Council must be prepared to impose new sanctions.
U.S. Secretary of State Rex Tillerson will chair a ministerial meeting of the Security Council on Friday to discuss tougher sanctions, which U.S. officials say could include an oil embargo, banning North Korea's airline, intercepting cargo ships and punishing Chinese and other foreign banks doing business with Pyongyang.
On Wednesday, Tillerson, Defense Secretary Jim Mattis, Director of National Intelligence Dan Coats and Joint Chiefs chairman General Joseph Dunford, are to hold a rare briefing on North Korea at the White House for the entire U.S. Senate.
U.S. Senator Lindsey Graham said he and fellow Republican John McCain had dinner with Trump on Monday and discussed North Korea. Graham told Fox News he was impressed by Trump's resolve.
"He's not going to let this nut-job in North Korea develop a missile with a nuclear weapon on top to hit America," Graham said, referring to North Korean leader Kim Jong Un.
"He (Trump) doesn't want a war any more than I do. But he's not going to let them get a missile. That's where they're headed and China needs to up their game to stop this before it's too late."
U.S. State Department spokesman Mark Toner said North Korea had become a "front and centre front-burner issue" and Tillerson would be "very vocal" on Friday about his concerns that countries were not doing enough to implement sanctions.
"We need to move more quickly and with greater determination to convince North Korea either to pursue denuclearisation or to apply enough pressure that it stops those activities," Toner told a telephone news briefing.
Japan's envoy on North Korea, Kenji Kanasugi, said he and his U.S. and South Korean counterparts agreed in talks in Tokyo on Tuesday that China should take a concrete role to resolve the crisis and could use an oil embargo as a tool.
The U.S. envoy for North Korea policy, Joseph Yun, said China had "a very, very important role to play" and South Korea's envoy, Kim Hong-kyun, said they had also discussed how to get Russia's help.
Japanese Prime Minister Shinzo Abe is expected to meet Russian President Vladimir Putin on April 27, the Kremlin said. It did not elaborate.
China, North Korea's sole major ally which nevertheless objects to its weapons development, has repeatedly called for calm, and its envoy for Korean affairs, Wu Dawei, was in Tokyo on Tuesday.
"We hope that all parties, including Japan, can work with China to promote an early peaceful resolution of the issue," Chinese foreign ministry spokesman Geng Shuang said.
North Korea's foreign ministry said the meetings called by U.S. officials reflected U.S. pressure that could "ignite a full-out war" and showed that Pyongyang's decision to become a nuclear power was correct.
The official China Daily newspaper said it was time to step back from harsh rhetoric.
"Judging from their recent words and deeds, policymakers in Pyongyang have seriously misread the U.N. sanctions, which are aimed at its nuclear/missile provocations, not its system or leadership," the newspaper said in an editorial.
"They are at once perilously overestimating their own strength and underestimating the hazards they are brewing for themselves."
Additional reporting by Ben Blanchard and Michael Martina in Beijing, Kaori Kaneko, Linda Sieg, Elaine Lies and Tim Kelly in Tokyo, Steve Holland, Matt Spetalnick, Susan Heavey and David Brunnstrom in Washington, and Vladimir Soldatkin in Moscow; Writing by Jack Kim; Editing by Robert Birsel and James Dalgleish