SEOUL (Dispatches) – A U.S. submarine has arrived in South Korea, amid worries of another North Korean missile or nuclear test.
The missile-armed USS Michigan is set to join an incoming group of warships led by aircraft carrier Carl Vinson.
North Korea celebrated its army's 85th founding anniversary on Tuesday. It marked the event with a large-scale firing drill, South Korea said.
Tensions have risen in the area in recent weeks, with the U.S. and North Korea exchanging heated rhetoric.
Experts fear Pyongyang could be planning more tests - it has marked some key anniversaries in the past with nuclear tests or missile launches.
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 U.S. 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 U.S. and Asia Pacific region.”
A statement from U.S. Naval Forces Korea described the submarine's visit as "routine deployment.”
"U.S. Navy ships and submarines routinely make port calls in a variety of locations," Lieutenant commander Matt Knight with U.S. 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."
Meanwhile, the White House has invited the entire U.S. 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.
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.