At least three foreigners have been abducted and a fourth killed by kidnappers in the centre of Mali's ancient tourist city of Timbuktu, security sources say.

The victim who was shot dead in Friday's attack had tried to resist his abduction, according to the sources who did not give the nationality of the hostages.

The kidnappers struck as the four were in a restaurant on the central square of Timbuktu, which is located in the country's north, the sources said.

The latest kidnapping came after two French nationals described as geologists were abducted by an armed gang from their hotel in the eastern village of Hombori near the border with Niger early on Thursday.

They had been sent by the company Mande Construction Immobiliere to take soil samples in the Hombori region where it plans to build a cement factory.

The attack took place at 1am (01:00 GMT) at the Dombia hotel.

A journalist for the AFP news agency in the Hombori region said at least a dozen French soldiers on a training mission in the region had been deployed to join Mali's army in the hunt for the pair.

Although there has been no immediate claim of responsibility, 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).

'Armed to the teeth'

AQIM has bases in the northern Mali desert from which it organises raids and kidnappings and deals in the trafficking of weapons and drugs.

The incident brings the total of foreigners held in the vast Sahel region to nine.

The captives, named in documents seen by AFP as Philippe Verdon and Serge Lazarevic, had arrived on Tuesday night.

Lazarevic, described by a witness as a large man while Verdon was said to be "more frail", had just completed their first day's work on the ground when they were kidnapped.

The watchman at the hotel said that "the kidnappers were armed to the teeth [...] I was tied up and told to point out the rooms of the Frenchmen, whom they brutally took away".

The kidnapping was "well organised", said a source in the security forces at Hombori. "We think that these people came from one of Mali's neighbouring countries to take part in the operation."

Northern Mali is classified as a "red zone" by the French authorities, which is a recommendation that travel there be avoided. Hombori is in the "orange zone" to the south, deemed less dangerous.