French forces have launched one of their largest offensives against what they claim to be extremist militants in the West African country, Mali.

Around 1,000 French soldiers have launched Operation Gustav to sweep a 20-kilometer river valley near the northeastern city of Gao.

The operation is said to be one of France's largest since its war in the former French colony began in January.

The offensive involves dozens of tanks, helicopters, drones and aircraft, said General Bernard Barrera, commander of the French land forces in Mali.

All access points to the valley, north of Gao, were closed and its ridges were made secure in the morning.

French soldiers along with Malian forces and police officers will spend the coming days combing the valley.

The French-led war in Mali has caused a serious humanitarian crisis and has displaced tens of thousands of people, many of whom reside in refugee camps in neighboring countries in deplorable conditions.

The people of northern Mali say the French war and the ruling junta are blocking the flow of humanitarian assistance to the war-affected areas.

A UN humanitarian official said on February 27 that Mali remains in dire need of humanitarian assistance.

About "200,000 children are not getting any education and haven't for the last year," said John Ging, director of operations for the Office for the Coordination of Humanitarian Affairs.