The journalists, who worked for the California-based Current TV, were detained by North Korean border guards on March 17 and put on trial behind closed doors earlier this month.

On June 8, the pair were sentenced to 12 years of hard labour on charges of entering the North illegally and engaging in "hostile acts".

Strained relations

North Korea said the two reporters had crossed illegally to its side of the border with China, although other reports have suggested the two were on the Chinese side when they were arrested.

The case has strained further already poor relations between the US and North Korea, following the secretive nation's nuclear test and several missile tests in May.

US and Japanese sources have said that North Korea could fire its most advanced ballistic missile towards Hawaii around the July 4 Independence day holiday in the US.

The US navy is also tracking a North Korean cargo ship off the coast of China which is believed to be carrying missiles and missile parts, the first such move under a new United Nations Security Council resolution which firms an earlier arms embargo and authorises ship searches.

North Korea has said it would view any such searches as an act of war.

Analysts say the women's sentences appeared unusually harsh and seemed to back up views that the journalists could be used as a bargaining chip by the North in its standoff with the US.