The Democratic Republic of Congo army said Sunday it has launched a new offensive against rebel fighters who fled to the hills after being ousted from their last stronghold. "We are pounding Mbuzi," one of three mountains in eastern DR Congo where the rebels are hiding, General Lucien Bahuma told AFP by telephone. "After the artillery we will send in the troops." Some 200 die-hard fighters of the M23 rebel group have been holed up in the mountainous region bordering Uganda since their base in the town of Bunagana was seized on Wednesday. "They are claiming back the hills. There is shooting in the mountains of Ntamugena, Mbuzi and Runyonyi. The rebels are fleeing," a DR Congo captain told AFP, speaking anonymously. The sound of heavy artillery could be heard from Kiwanja, a town around 20 kilometres (12 miles) away. The M23 movement was founded by ethnic Tutsi former rebels who were incorporated into the Congolese army under a 2009 peace deal but then mutinied in April 2012, claiming that the pact had never been fully implemented. At their strongest in November last year, M23 marched into Goma, a mining hub and city of one million people, and took control for 10 days, before regional leaders persuaded them into fresh peace talks. But the stop-start talks fell apart last month when Kinshasa refused amnesty for about 80 rebel leaders and the DR Congo army -- backed by a special United Nations force -- went on the attack in a bid to end the rebellion once and for all.