Senegalese forces are ready to take on a greater role in Mali as French-led efforts to root out Islamist rebels evolve, Senegalese President Macky Sall said  during a visit to Washington. Until now, Senegalese forces had not been in direct contact with rebel fighters, but were moving toward the key city of Gao in the war-wracked north of Mali and the fabled desert city of Timbuktu, Sall told AFP in an interview. Seven people were killed in clashes between the Malian army and Islamists in Gao on Sunday, according to an African security source. "We must hold them back, maintain our positions, ensure that the local population is safe and confront suicide attackers," the Senegalese leader said, calling such assailants the main threat in the west African country. In a surprise intervention, France sent troops to Mali in January to prevent an advance on the capital Bamako by Al Qaeda-linked fighters who overran northern Mali a year ago, taking advantage of a vacuum left after a coup. France, which has 4,000 troops in the country, is eager to withdraw and hand over to an African force, known as AFISMA, which would be transformed into a UN peacekeeping mission. UN Secretary General Ban Ki-moon says up to 11,200 peacekeepers could be needed. Senegal is expected to contribute 650 men. "Now it's time to transform this force into a United Nations force. We want to see a very clear mandate, and for the United Nations to take up the mantle," Sall said. "France has already done most of the job." French President Francois Hollande said Thursday that French troops would begin to pull out at the end of April. Having been beaten out of Mali's northern cities, the Islamists have retreated to desert and mountain hideouts from where they launch guerrilla attacks on French, Chadian and Malian forces trying to flush them out. Ansar Dine, which occupied northern Mali last year with two other Islamist groups, has vowed to continue its fight to drive out French and African troops. Sall was one of four African leaders to meet Thursday at the White House with US President Barack Obama, who praised them as symbols of democratic success that could lead an emerging continent. The Senegalese leader, who was elected just a year ago, said the comments served as "encouragement for what I've been doing as the head of state in Senegal -- reinforcing democracy, the rule of law and good governance."