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By Inal Ersan

DUBAI, March 13 (Reuters) - Al Qaeda's North African wing threatened on Thursday to kill two Austrian hostages it had abducted in Tunisia if Vienna failed to secure the release of some of the group's members jailed in Tunisia and Algeria.

The three-day ultimatum starts at midnight on Thursday, al Qaeda in the Islamic Maghreb said in a statement posted on an Islamist Web site.

Austrian Foreign Minister Ursula Plassnik said efforts were being made to secure the release of the hostages but noted that the demands were outside Vienna's jurisdiction.

"Austria would be responsible for the lives of the two hostages should the deadline come and our demands are not met," the militant group said.

"As you care for the safety of your citizens, we care to free our brothers who face the ugliest forms of torture at the prisons of Tunisia ... and Algeria," it said.

"We ask the families of the hostages and the Austrian public opinion to press their country's (government) to meet the demands of the mujahideen to preserve the lives of the two tourists," it added.

The demands and a list of the names of the group's prisoners were sent to Vienna through unidentified mediators, it said in the posting, which had pictures of the hostages identified in Austrian media as Andrea Kloiber, 43, and Wolfgang Ebner, 51.

The group, which has been waging a violent campaign against government forces and foreign interests in North Africa, said its members were jailed for confronting "the new crusade against Islam".

Plassnik confirmed that Vienna had received the demands. "They (kidnappers) have taken up contact with the Austrian side. Political demands have been made whose fulfilment do not fall within the responsibility of the Austrian side," she said in a statement.

"Appropriate efforts are being made to obtain the return of both hostages to Austria unharmed," Plassnik said.

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The hostages, who went missing last month during a trip to Tunisia, appeared in the pictures dressed in robes and surrounded by militants in a desert area. Their captors were armed with assault rifles and rocket-propelled grenade launchers.

The face of the woman, who wore a blue headscarf was digitally blurred, apparently to abide with an austere interpretation of Islam which says women should cover their faces.

Al Qaeda has said it seized the two hostages on Feb. 22 and warned Western tourists not to visit Tunisia. The new statement expanded the warning to include other Maghreb states -- Morocco, Mauritania and Algeria.

An Algerian newspaper said on Tuesday that the Austrian tourists have been moved by their kidnappers to Mali across the Sahara desert.

A senior security source in Mali said it was possible the kidnappers had moved to the northern desert town of Tessalit, where the al Qaeda wing -- formerly known as the Salafist Group for Preaching and Combat (GSPC) -- is believed to have a base.

The GSPC kidnapped 32 European tourists in the Sahara in early 2003 and held some of them for six months. When they were eventually released in northern Mali, media reports said the German government had paid $5 million for their release.

Analysts have said the fact the kidnappers had announced the abduction suggested they were ready to negotiate and pointed out that the group had seized hostages to raise money in the past.

Al Qaeda has linked its action to an Israeli offensive in Gaza, saying "our folk in Gaza are being slaughtered by the Jews with consent from Western countries."

Israel last week ended an offensive which killed 120 Palestinians in Gaza. (Additional reporting by Mark Heinrich in Vienna; Editing by Dominic Evans)

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