The United States has sent a nuclear submarine to South Korea amid escalating tensions with the neighboring North.
Washington has already sent the USS Carl Vinson aircraft carrier strike group to the western Pacific Ocean.
The Ohio class submarine will later join the aircraft carrier for exercises in the Sea of Japan.
The movement came after North Korea threatened to sink USS Carl Vinson.
"Our revolutionary forces are combat-ready to sink a US nuclear-powered aircraft carrier with a single strike," the ruling Workers' Party's newspaper said in a commentary on Sunday.
The article said Pyongyang had weaponry that "can reach continental US and Asia Pacific region."A statement from US Naval Forces Korea described the submarine's visit as "routine deployment."
"US Navy ships and submarines routinely make port calls in a variety of locations," Lieutenant commander Matt Knight with US Pacific Fleet told Fox News.
"As a matter of routine, we do not discuss future operations or the details regarding the operations of our submarines. USS Michigan is currently on a routine deployment to the Indo-Asia-Pacific."
'Senate to go to White House for North Korea briefing'
Meanwhile, the White House has invited the entire US Senate on Wednesday for a briefing on the mounting tensions between Washington and Pyongyang.
The briefing will be delivered by several top officials including Secretary of State Rex Tillerson, Secretary of Defense Jim Mattis, Director of National Intelligence Dan Coats and General Joseph Dunford, chairman of the Joint Chiefs of Staff, White House spokesman Sean Spicer said on Monday.
'UN must impose new sanctions on N Korea'
President Donald Trump has said the United Nations Security Council must impose new sanctions on North Korea.
"The status quo in North Korea is also unacceptable and the council must be prepared to impose additional and stronger sanctions on North Korean nuclear and ballistic missile programs," Trump said on Monday ahead of a lunch with ambassadors from countries on the Security Council.
"This is a real threat to the world, whether we want to talk about it or not. North Korea is a big world problem and it's a problem that we have to finally solve," he added.
North Korea has so far conducted five confirmed nuclear tests and numerous missile test-launches. While it has not fired missiles against other countries, it has vowed strong action -- including missile attacks against South Korea -- if it is invaded by the South and the US.
The US earlier threatened to strike North Korea if it tried to test-fire an intercontinental ballistic missile. And, Pyongyang warned the US of an "all-out war" and announced that it would continue to test missiles on a weekly basis.