US Secretary of State Hillary Clinton arrived Wednesday for a visit aimed at showing strong support for South Korea following a deadly naval attack blamed on North Korea.
She and Defense Secretary Robert Gates were Wednesday morning to visit the Demilitarised Zone dividing the two Koreas, before paying tribute to 46 South Korean sailors killed when their warship sank in March.
They were to hold "two plus two" talks on Wednesday afternoon with South Korean counterparts.
South Korea, its US ally and other countries, citing findings of a multinational investigation, accuse the North of torpedoing the Cheonan corvette near the disputed sea border -- a charge it denies.
The incident has sharply raised tensions on the peninsula. Gates and his South Korean counterpart Kim Tae-Young Tuesday announced major joint naval exercises starting this Sunday as a deterrent to the North.
The July 25-28 drill in the Sea of Japan will involve about 20 ships including the 97,000-ton aircraft carrier USS George Washington, some 200 fixed-wing aircraft and around 8,000 service personnel.
The drill is the first in a series designed "to send a clear message to North Korea that its aggressive behaviour must stop", Gates and Kim said.
The "two plus two" meeting was originally scheduled to mark the 60th anniversary this year of the start of the 1950-53 Korean war, in which a US-led United Nations force defended the South.
"Following the attack on the Cheonan I think it's particularly timely to show our strong support to South Korea, a stalwart ally, and to send a very clear message to North Korea," Clinton told reporters Tuesday before leaving Afghanistan.
Wednesday's visit "is a real show of solidarity", she said.
Clinton said the United States had since the start of the Obama administration offered the North a different path -- on condition it scraps its nuclear weapons.
The DMZ, whose approaches are guarded by minefields and razor wire, has bisected the peninsula since the 1950-53 conflict ended only in an armistice and not a peace treaty, leaving South and North technically at war.
The US has stationed troops in the South ever since, and currently has 28,500 posted there.
The man nominated to head the US spy community told US senators Tuesday that he fears a period of direct attacks by North Korea on its southern neighbour.
James Clapper was making a written response to questions by members of the Senate Intelligence Committee.
"The most important lesson for all of us in the intelligence community from this year's provocations by Pyongyang is to realise that we may be entering a dangerous new period when North Korea will once again attempt to advance its internal and external political goals through direct attacks on our allies in the Republic of Korea (South Korea)," Clapper wrote.
After their DMZ visit Gates and Clinton were to visit the War Memorial in Seoul to pay tribute both to the war dead and the Cheonan victims.
Following the afternoon talks the two sides were to issue a joint statement expected to touch on ways to strengthen the alliance and deal with North Korea.