An armed gang of kidnappers has abducted three Europeans and killed a fourth in the city of Timbuktu in northern Mali, security sources said.The hostages' nationality is not known.The man was shot dead trying to resist the gang, reports say. Reuters news agency quoted an unnamed government source as saying he was German.It comes a day after two French geologists were abducted by an armed gang from their hotel in the eastern village of Hombori.It is believed to be the first time foreigners have been abducted in the ancient city of Timbuktu, a popular destination for tourists.The kidnappers struck as the four were in a restaurant on its central square, AFP news agency reported, quoting security sources.The incidents are the latest in a series of abductions of foreigners believed to be the work of Al-Qaeda in the Islamic Maghreb (Aqim).Aqim has bases in the northern Mali desert from which it organises raids and kidnappings, and traffics weapons and drugs.French soldiers have joined Mali's army in the hunt for the French pair kidnapped in Hombori, according to AFP.The couple were the first Westerners in Mali to be kidnapped south of the River Niger.Al-Qaeda linked fighters have in the past brought hostages into northern Mali from neighbouring countries, such as Niger where four French nationals - still being held - were kidnapped in September 2010.Huge swathes of the Sahel region south of the Sahara Desert have been rendered off-limits to foreigners.