Georgia's breakaway South Ossetia region on Thursday prolonged the detention of Georgian teenagers who allegedly crossed into rebel-held territory with explosives.

The youths, between 14 and 17 years old, will be held in - pre-trial detention for one month and 20 days - the region's interior ministry said in a statement.

The teenagers were detained on November 4 and later charged with carrying explosives and crossing the border illegally. The case has aroused concern in the West.

Georgian President Mikheil Saakashvili called the US Vice President Joe Biden and urged Washington to work - for the immediate and unconditional release of the detained minors - the Georgian foreign ministry said in statement.

Georgia has accused the separatist administration of "kidnapping" the boys from a village near the de-facto border with South Ossetia and demanded their immediate release.

- The teenagers were arrested by the Russian occupiers without any legal grounds - Georgian Reintegration Minister Temur Yakobashvili told AFP, adding that - we demand their immediate and unconditional release. -

Yakobasvili placed the blame for the detentions on Russia.

The US Assistant Secretary of State Michael Posner said in Tbilisi on Wednesday that there was "no basis" for the detentions and the boys should be freed - as quickly as possible, immediately. -

The European Union in a statement last week expressed "deep concern" over the detention of Georgians in South Ossetia, citing case of the four minors, and urged - for a rapid release of all detained persons. -

Tensions remain high around South Ossetia following last year's Georgia-Russia war over the breakaway region.

The five-day war in August 2008 saw Russian troops and tanks pour into Georgia to repel a Georgian military attempt to retake control of South Ossetia, which had received extensive Russian backing for years.

Days after the conflict, Russia recognised South Ossetia and another rebel Georgian region, Abkhazia, as independent, a move that has so far been followed by only Nicaragua and Venezuela.