The Central Court, the North’s highest court, held the trial of the two Americans — Laura Ling and Euna Lee — from Thursday to Monday and convicted them of “committing hostilities against the Korean nation and illegal entry”, the North’s official news agency, KCNA, said in a report monitored in Seoul.

Ling and Lee were detained by North Korean soldiers patrolling the border between China and the North on March 17.

US Secretary of State Hillary Clinton has called the charges “baseless” and the Government had demanded that the North release the two women.

The sentence, which cannot be appealed, came amid rising tensions between Washington and Pyongyang. Earlier on Monday, North Korea threatened to retaliate with “extreme” measures if the UN punished it for its nuclear test last month, and Washington warned that it might try to restore the North to its list of states that sponsor terrorism, a designation that could subject the state to more financial sanctions.

Ling and Lee were on a reporting assignment from Current TV, a San Francisco-based media company co-founded by Al Gore, the former Vice-President, when they were detained by the soldiers. The reporters were working on a report about North Korean refugees — women and children — who had fled their homeland in hopes of finding food in China.

Analysts said they were pawns in a rapidly deteriorating confrontation between the US and North Korea — a potential bargaining chip for the Pyongyang regime and a handicap for Washington.

Ling is said to suffer from an ulcer and needs medication. Lee has a four-year-old daughter at home.