ACCRA (Reuters) - French President Emmanuel Macron fears Islamist militants have scored military and symbolic victories in West Africa while a regional military force has struggled to get off the ground, a French presidential source said on Thursday.

To help get the new G5 Sahel force operating effectively, he said, France has invited the United States to a summit with the five participating countries as well as the African Union and European Union in Paris next month.

Thousands of U.N. peacekeepers, French troops and U.S. military trainers and drone operators have failed so far to stem a growing wave of jihadist violence, leading world powers to pin their hopes on the new G5 Sahel force.

The G5 Sahel initiative - grouping Burkina Faso, Chad, Mali, Mauritania and Niger - faces an immense security challenge in a largely desert and weakly governed region and already faces questions over its financing and provision of equipment.

“Emmanuel Macron believes that it’s not going quickly enough and that the terrorists have registered military and symbolic victories, especially in Niger, and (that) it’s urgent to reverse this trend,” the French official said in Ghana where Macron was winding up a three-day Africa trip.

“The (objective) will be to accelerate the calendar for the support of the force, and the operational calendar.”

The jihadist threat hit home again last month with an attack in Niger in which eight U.S. and Nigerien troops were killed, prompting American officials to forecast that U.S. involvement in the Sahel region would deepen.

As well as the leaders of the G5 nations - all former French colonies - and the EU and African Union, the French presidential official said the United States had also been invited to the Dec. 13 summit.

The G5 force is to eventually comprise 5,000 men from seven battalions and police the region in collaboration with 4,000 French troops deployed there since Paris intervened in 2013 to beat back an insurgency in northern Mali.

It will also have to coordinate with MINUSMA, Mali’s U.N. peacekeeping mission. MINUSMA has been frequently attacked in the north where Islamists have regained ground since 2013.

A donor conference will be held in Brussels on Dec. 14 to raise funds for the Sahel force. Paris has also asked Saudi Arabia to help finance the force and representatives of the kingdom could also be in Paris on Dec. 13, the official said.