Rebel groups are making new gains in eastern DR Congo after Indian UN troops abandoned positions near a regional capital, according to an internal UN document seen by AFP.

The UN mission in Democratic Republic of the Congo (MONUSCO), which is being being wound down, said in a note to staff that "the current security situation is becoming increasingly volatile as M23 has reached the northern outskirts of Sake."

Sake is about 25 kilometres (15 miles) from Goma, the largest city in North Kivu province where the population has doubled to two million as refugees flee the advance of the M23 rebel group.

According to the MONUSCO note, M23 forces have occupied at least three positions around Sake "since their abandonment by INDRDB," referring tO the Indian contingent.

M23 and DR Congo forces exchanged artillery fire throughout the weekend around Sake and the western outskirts of Goma, residents said.

After eight relatively quiet years, M23 rebels in 2021 resumed their campaign to seize territory in eastern DR Congo.

The DR Congo government, the United Nations and Western countries accuse Rwanda of backing M23, but the Rwanda government denies any involvement in the conflict.

The 15,000 UN troops deployed in DR Congo started to leave in February at the request of the Kinshasa government which considers them ineffective. The withdrawal is due to be completed by the end of the year.