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There have been clashes between Mauritanian troops and al-Qaeda militants in the Sahara desert in northern Mali, reports say.

A dozen militants are said to have been killed in the fighting in Raz-el-Ma, 250km (155 miles) west of Timbuktu.

Mauritania has also sent combat aircraft into the battle, security sources said.

France has denied the raid is connected to the kidnapping in Niger of seven foreigners earlier this week.

A foreign ministry spokesman in Paris said the fighting was "independent" of the kidnapping adding: "There are no French forces in the field."

The weapons used by both sides indicate they have been preparing for a heavy battle, says the �鶹Լ��'s North Africa correspondent Chloe Arnold.

"The Mauritanians have engaged at least two combat aircraft with the aim of gaining the upper hand, which they have not had so far," the security source told AFP news agency.

Initial reports of the military operation said the fighting was taking place near the border with Mali's Timbuktu region, quoting Mauritanian security sources.

Later, the same sources told the AFP news agency: "We are presently in Malian territory and engaged in full combat."

Five Mauritanian soldiers have also been killed in the clashes, reports say.

Raz-el-Ma is a remote town, normally home to nomadic Tuareg tribesmen.

The fighting is the latest in a series of clashes between Saharan countries and al-Qaeda in the Islamic Maghreb (AQIM), which is the chief suspect in the kidnapping of seven foreigners in Niger earlier this week, our correspondent adds.

Mauritania's armed forces have an agreement with Mali to patrol the largely lawless desert areas that cross both countries to pursue suspected militants.

Earlier this year, four Sahara states set up a joint military headquarters in the south of Algeria, to improve co-ordination between the states in combating al-Qaeda.

But security experts say this weekend's violence in northern Mali shows al-Qaeda is intensifying its activities in the region.

Prime suspect

France suspects AQIM of being behind the kidnapping of seven uranium workers in Niger on Wednesday night, including five French nationals.

The hostages were contracted by the French company Areva, which mines uranium in the region, and are believed to have been taken to Mali.

They were seized from their homes near the Areva uranium mine at Arlit, about 800km (500 miles) north-east of Niger's capital Niamey.

The French foreign ministry said it had received no claim or ransom demand and could not draw a definitive conclusion about the kidnappers.

However, Foreign Minister Bernard Kouchner told French radio that "one could imagine it's the same group, at least the AQIM movement".

AQIM has kidnapped French and other Europeans nationals in the past. It has also previously moved its hostages to the Malian desert.

The group emerged in 2007 after an Algerian militant group, the Salafist Group for Preaching and Combat (GSPC), aligned itself with Osama Bin Laden's international terror network.

It has carried out suicide attacks and ambushes in Algeria, and in recent years become more active in the Sahara, where governments struggle to impose their authority.

In July, AQIM said it had killed Michel Germaneau, a 78-year-old French hostage being held in Mali, after a cross-border raid involving French and Mauritanian troops failed to free him.

The group also killed the British hostage, Edwin Dyer, last year after the UK government refused to give in to its demands.