Riyadh, May 18 (DPA) Two German girls who were part of a group kidnapped in Yemen last year have been transferred to the Saudi authorities, a spokesperson for the Saudi interior ministry said Tuesday.

The two girls were found during a joint Yemeni-Saudi operation, spokesperson Mansour al-Turki told DPA.

"It was a secret security operation launched based on information acquired by the Saudi forces," al-Turki said.

The two girls were transferred across the border into Saudi Monday, al-Turki said. He added that they are now investigating more information they have concerning the rest of the hostages.

The pair were freed by Saudi special forces in an operation targeting the hideout of their abductors in Yemen, Yemeni tribal sources said earlier.

The rescue raid in which Saudi military helicopters took part was carried out in the Shada district of the north-western Yemeni province of Saada province Monday afternoon, the sources told DPA.

The girls are currently undergoing medical check-ups, and the German embassy in Riyadh has been informed of the case.

"We are relieved that the Saudi forces have succeeded in freeing two of our five kidnapped citizens in Yemen. The two girls are currently in the safe keeping of the Saudi authorities. In the circumstances, they are doing well. They are due to return to Germany tomorrow," German Foreign Minister Guido Westerwelle said in a statement.

"We are exerting all our efforts to clarify the situation regarding the remaining hostages. Their fate continues to give us the utmost concern. We are hoping for a happy outcome, and will continue to do everything possible towards that end," he added.

The girls were part of a group of foreigners who were kidnapped in Yemen's troubled north-western Saada province last year.