Heavy casualties in northern Mali

At least 13 Chadian soldiers have been killed in fighting in northern Mali, the heaviest casualties sustained by French-led African troops since the launch of a military campaign against rebels last month, Chad's army has said. It said Friday's clashes occurred in the Ifoghas mountains, where many militants are believed to be hiding.

Last month France led an operation to help oust Islamists who seized the vast northern region of Mali in 2012.

Thousands of soldiers from African countries have also been deployed in Mali since then.

Islamist rebels are believed to have retreated to the Ifoghas mountains - a desert area in the Kidal region near the border with Algeria - after being forced from northern population centres in recent weeks.

In a statement issued late on Friday, the Chadian army said it had "destroyed five vehicles and killed 65 jihadists", adding that 13 of its soldiers had been killed and another five wounded.

Earlier this month, some 1,800 Chadian soldiers began patrolling the city of Kidal.

Chad has pledged to send 2,000 troops to Mali as part of the African-led mission.

Fighting between Islamist insurgents and Malian troops - backed by French soldiers - also continued in the central city of Gao.

On Thursday, the coalition said it had recaptured the city hall, which had been seized by militants a day earlier.

In a separate development, US military said it had deployed surveillance drones in Niger to gather information on Islamist militants across the border in Mali and share intelligence with French troops.

The US said a 100-strong contingent was operating the drones out of a base in Niger.

France intervened in January in its former colony, fearing that al-Qaeda-linked militants who had controlled Mali's north since April 2012 were about to advance on the capital Bamako.

The French have said they are planning to start withdrawing their 4,000 soldiers next month, and would like the African-led contingent to become a UN peacekeeping operation.