An ultimatum set by Islamic militants holding two Austrian tourists in the African nation of Mali expired at midnight Sunday with no official word from the captors.

Austrian officials in Vienna expressed hope Monday that negotiations to secure the release of the two, Andrea Kloiber and Wolfgang Ebner, who disappeared February 22 while vacationing in Tunisia will continue.

Al-Qaida's North African branch demanded a ransom and the release of Islamic militants jailed in Algeria and Tunisia in exchange for the two Austrians.

The group also warned that any attempt to free the hostages by force will lead to their immediate execution.

The kidnappers initially set a March 16 deadline for talks but postponed it at the last minute in an Internet statement posted a week ago.

Meanwhile, authorities in Mali say clashes between Tuareg rebels and government troops near the border with Algeria have killed three soldiers since Thursday.

They said several troops were wounded and at least 29 captured in the rebel attacks in Mali's Kidal region - the same area where the militants are reported to be holding the two Austrians.

Some information for this report was provided by AFP, AP.