U.S. troops in South Korea put on alert as tensions rise over sinking ship

Barack Obama yesterday ordered that the 28,000 U.S. troops in South Korea be put on alert as tensions with North Korea escalated.

The U.S. President demanded that Pyongyang apologise for sinking a South Korean warship in March and punish those responsible.

International investigators blame North Korea for sinking the Cheonan ship, killing 46 sailors. The Pentagon said it will start joint anti-submarine and military drills with South Korea ‘in the near future’ as a result of the findings.

Threat: South Korean soldiers jump out from a military truck during an anti-terror drill in downtown Seoul yesterday

Vow: South Korean President Lee Myung-bak bows after delivering a speech at the War Memorial of Korea yesterday, in which he warned that North Korean would pay the price for the sinking of a navy ship in a surprise attack

U.S. support for South Korea was ‘unequivocal’, White House spokesman Robert Gibbs added.

‘We endorse [President Lee Myung-bak’s] demand that North Korea... stop its belligerent and threatening behaviour,’ he said.

The U.S. is reportedly bringing forward deployment of a hightech F-22 Raptor ground-attack aircraft to Japan this month.

Should conflict erupt, it could reach North Korea within minutes.

North Korea threatened to fire at equipment from which South Korea planned anti-Pyongyang broadcasts. President Lee said he would not hesitate to retaliate.

The U.S. backs the Lee plan to bring the issue to the UN Security Council and would work with allies to ‘reduce the threat’.

Trigger: Navy personnel stand guard last week near the wreckage of the naval vessel Cheonan, which was sunk on March 26 near the maritime border with North Korea

U.S. Secretary of State Hillary Clinton, who is in talks in China, said the situation was ‘highly precarious’.

The row centres on the sinking of the South's Cheonan corvette in March, killing 46 sailors in one of the deadliest clashes between the two countries since the 1950-53 Korean War.

In a sombre televised address to the nation, President Lee said if his country's waters, airspace or territory were violated he would 'immediately exercise our right of self-defence.'

He added: 'I solemnly urge the authorities of North Korea ... to apologise immediately to the Republic of Korea (South Korea) and the international community.'

State of war: South Korean soldiers check speakers, which were used to broadcast propaganda toward North Korea

Fears: A Korean man watches a live broadcast of the president's speech yesterday as tensions between the two Koreas increased

The two Koreas are still technically at war and have more than 1million troops near their border.

In the past the South has tolerated the North's outrages such as the downing of a South Korean airliner in 1987, which killed 115 people.

But this time the mood is far tougher and it has banned all trade, investment and visits with North Korea.

'North Korea will pay a price corresponding to its provocative acts,' said President Lee, adding that he would be operating a principle of 'proactive defence'.

'North Korea's goal is to instigate division and conflict. It is now time for the North Korean regime to change'.