North Koreans take part in a mass rally in central Pyongyang to mark the 60th anniversary of the Korean War on Friday

Tens of thousands of North Koreans rallied in their capital to condemn the United States and South Korea on the 60th anniversary of the start of the Korean War, while Seoul told Pyongyang to admit responsibility for a deadly warship sinking.

One large poster at the rally in Pyongyang depicted a man kicking an American soldier and the slogan "US Army, Get Out". Another sign said, "Kick Them Out With a Single Punch", according to footage shot by broadcaster APTN.

At least 120,000 people marched through the streets, "raising shouts for hatred and wrath at the US imperialists and the South Korean group of traitors kow-towing to them", according to the official Korean Central News Agency.

The mood surrounding the 60th anniversary of the war's outbreak is far different from that at the 50th, which came just days after the conclusion of the first-ever summit between the Koreas in Pyongyang.

Tensions are high following the March sinking of the South Korean warship Cheonan in which 46 sailors died. South Korea has blamed the North for the attack, which Pyongyang denies. Relations were already sour since conservative president Lee Myung-bak took office in 2008 in Seoul with a harder line toward the North than his liberal predecessor.

The Korean conflict started in the early hours of 25 June 1950, with an attack on the South by North Korean troops. The Korean peninsula had been divided in 1945 after colonial ruler Japan's defeat in World War II.

The US and 15 other countries sent troops to aid South Korea, while Chinese soldiers fought with the North and the Soviet Union provided air support. Three years of combat devastated both sides. The fighting ended with an armistice, not a permanent peace treaty, leaving the peninsula in a technical state of war.

At yesterday's Pyongyang rally, North Korean soldiers and civilians crammed the city's central square to shout slogans and listen to a speech condemning the US, the APTN footage showed.

"In order to establish our people's dignity and our country's autonomy, our people and army will continue to strengthen nuclear deterrence for self-defence," Kim Ki Nam, secretary of the Central Committee of North Korea's Workers' Party, told the gathering.

North Korea, which has carried out two underground nuclear tests, often trumpets its success in atomic development as its ultimate means of defence and guarantee of independence.

The isolated nation's leader Kim Jong Il was not seen at the event, which took place in Kim Il Sung Square.