A South Korean soldier looks out at North Korea as he stands guard on the border island of Baengnyeong on Tuesday. North Korea has raised its level of military readiness after being blamed for a deadly warship attack in March. ((Ahn Young-joon/Associated Press))

North Korean military forces will respond if the UN Security Council questions or condemns the country over the sinking of a South Korean navy ship, the country's UN ambassador said Tuesday.

South Korea's accusations that North Korea torpedoed the ship in March, killing 46 sailors, have created "a touch-and-go situation," said ambassador Sin Son-ho at a rare news conference at United Nations headquarters in New York.

"War may break out at any time," the ambassador warned. "If the Security Council release[s] any documents against us condemning or questioning us ... follow-up measures will be carried out by our military forces."

North Korea vehemently denies sinking the ship.

Pro-unification and anti-war activists shout slogans in front of the U.S. Embassy in Seoul Tuesday during a rally commemorating the 10th anniversary of the North-South talks that led to the document known as the June 15 declaration, considered a step toward reunifcation. ((Jo Yong-Hak/Reuters)) Sin accused South Korea and the United States of cooking up the accusation against the North and demanded that military investigators from Pyongyang be permitted to go to the site of the sinking, which the South has refused to allow.

Forty-six sailors died in the frigid Yellow Sea waters near the Koreas' maritime border while 58 were rescued. It was South Korea's worst military disaster since the end of the three-year Korean War in 1953.

Fragments recovered from the area indicate the torpedo came from North Korea, a team of international investigators said in May.

Meanwhile, thousands of South Koreans donned gas masks Tuesday in a nationwide civil defence drill as Seoul's defence chief said North Korea has bolstered its military readiness amid tensions over the sinking of a South Korean warship.

The defence drill was the first on a nationwide scale for possible chemical, biological and radiological attacks since 1989.