KINSHASA (Reuters) - Two military helicopters crashed in a strife-torn part of eastern Democratic Republic of Congo with at least four crew members on board, authorities said on Monday.

Government spokesman Lambert Mende told Reuters it was not clear what brought down the helicopters on Friday in North Kivu province near the borders with Rwanda and Uganda.

Over the weekend, U.N.-sponsored Radio Okapi cited military sources as saying that the helicopters crashed while pursuing fighters from the former Congolese rebel group M23. An army spokesman declined to comment.

The M23 was the largest of dozens of armed groups in the country and controlled huge swaths of eastern Congo in 2012 and 2013 before it was defeated by Congolese and U.N. forces.

Reports of a possible M23 revival by former fighters held in camps in Uganda and Rwanda have surged in recent weeks. On Monday, Rwanda’s defense ministry said in a statement that a group of about 30 unarmed people claiming to be M23 and fleeing combat with Congo’s army crossed the border at the weekend.

Mende said he had not yet seen the statement.

Earlier this month, Uganda’s government said it had detained more than 100 former M23 rebels trying to return to Congo from camps in Uganda where they have been awaiting amnesties. Congo said the fighters had encroached onto Congolese territory.

Radio Okapi also reported that five crew members - three Russians and two Congolese officers - were rescued and brought to hospital. Mende said he could not confirm that information.

Millions died in regional conflicts in eastern Congo between 1996-2003, most from hunger and disease, and dozens of armed groups continue to fight over natural resources and prey on the civilian population.