M23 rebels
A M23 rebel fighter looks on as he mans a position in Bunagana, in North Kivu on the border with Uganda, in June 2012 MICHELE SIBILONI/AFP/GettyImages

Officials of the Ugandan military have said they clashed with M23 rebels, the former largest armed group in neighbouring Democratic Republic of Congo (DRC), who have recently been moving across the porous borders between the two countries.

For weeks now, skirmishes between the Congolese army (FARDC) and M23 fighters have highlighted fears of a potential revival of the rebel group, which was defeated in 2013 in the lush hills along the border with Uganda and Rwanda.

In the latest bout of violence, the Uganda People's Defence Force (UPDF) clashed with an unknown number of M23 fighters on Wednesday (22 February) in the Bisanga region, in Western Uganda.

Following the fighting, several fighters crossed the border into neighbouring Uganda to find shelter, according to RFI. Richard Karemire, spokesman of the UPDF, confirmed that some 44 M23 fighters surrendered to the Ugandan army.

It remains unclear whether these fighters were part of a large group which, in January, had fled the disarmament camps where they had been confined since their 2013 defeat.

Calm returned to the Bisanga border locality on Wednesday evening, according to Karemire. According to reports, civilians displaced by the clashes also crossed the border into Uganda. Their number remains unclear.

On the other side of the border, RFI quoted a military source as saying that a group of M23 fighters was believed to be active near Tshanzu, in restive North Kivu province near the border between the two countries. Military operations are currently underway, the source said.

On Wednesday, the United Nations peacekeeping mission to DRC (Monusco) confirmed it had "launched aerial surveillance against a probable presence of elements of the former M23". In a tweet, the mission added: "Monusco is working with its military partners to identify places where armed groups may be hiding."

Previously operating as the biggest of a dozen armed groups in the country, M23, a mostly Tutsi-led rebel group, brought havoc to eastern DRC between April 2012 and November 2013 as it fought to control of swathes of land in the African nation's mining heartland.

Accused of being responsible for a series of murders, rapes and forced recruitment of children, the group was defeated in eastern DRC in late 2013, after a 20-month campaign led by the Congolese army and backed by thousands of UN fighters.