Fighting erupted again late on Saturday between eastern Congolese rebels and the army, which said it would push on with an offensive to recapture all territory controlled by insurgents despite their call for a ceasefire.

Democratic Republic of Congo’s army, backed by a new UN brigade with an unprecedented mandate to launch attacks, has forced M23 rebels to retreat from positions they have held for months overlooking the eastern city of Goma.

Some shells fired during recent fighting have landed in neighbouring Rwanda, threatening to pull the small but militarily powerful country openly into the conflict.

Both Congo’s army and rebels have accused each other of firing the missiles. Both sides said fighting erupted several kilometres north of Kibati, on hilltop positions seized from rebels – the latest in nearly two decades of unrest fuelled by ethnicity, local politics and competition over land and mineral wealth.

“The rebels are criminals and we are obliged to pursue them. We want to recapture all of the territory they currently occupy and restore the authority of the army and state,” said Congolese army spokesman Lt Colonel Olivier Hamuli.

In a statement sent to journalists, M23 confirmed the resumption of fighting and complained it came despite a pullback by its troops and an offer of a ceasefire.