Saudi Arabia's security forces have freed two German girls held hostage in neighbouring Yemen, an interior ministry spokesman said on Tuesday, but there was no word on the fate of four other hostages seized alongside them.

"Saudi Arabia has retrieved two German children kidnapped in Yemen," a Saudi interior ministry spokesman said. "The two children were in a border area between the two countries among a group previously kidnapped by criminal elements last year."

A German family of five and a Briton have been missing in Yemen since last June, held by kidnappers who the government believes have links to al Qaeda. There was no immediate word on the fate of the other hostages.

The missing Europeans were among a group of nine foreigners kidnapped in the northern region of Saada, of which three women - two Germans and a South Korean -- were later found dead.

The German embassy in Riyadh said the girls were being taken for medical checks, according to the Saudi state news agency.

No group has claimed responsibility for the abduction, which occurred in an area where Shi'ite rebels have been fighting government troops on and off since 2004. The rebels have denied carrying out the kidnapping.

That conflict, which drew in oil exporter Saudi Arabia in November, appears to have calmed down following a ceasefire agreement but analysts say peace is unlikely to last.

Yemen is under pressure to contain al Qaeda after the Yemeni-based regional arm of the militant group claimed responsibility for an unsuccessful attempt to bomb a U.S.-bound passenger plane in December.

Western allies and Saudi Arabia fear al Qaeda is exploiting instability in Yemen to use the country as a base from which to prepare attacks in the region and beyond.