The UN special force in the eastern Democratic Republic of Congo engaged in direct combat with besieged M23 rebels on Monday, throwing its weight behind a crushing army assault despite calls for a truce.
A UN source said the intervention brigade fired mortar rounds after getting the "green light" to bombard the last positions of the M23, in what appeared to be the first time the force has actively taken part in the fighting since the army launched its offensive late-October.
"Our targets are... Runyonyi and Chanzu," said another source in the UN brigade, referring to two hilltops about 80 kilometres north of regional capital Goma, at about 2,000 metres (6,500 feet), where dozens of holdout rebels have dug in.
"There is some resistance. We will continue to fire until everything is under control," added the source.
Until now, the UN intervention brigade had been backing the Congolese forces with aerial reconnaissance, intelligence and planning.
News of the UN force's intervention came hours after the Congolese army said it had seized a key rebel position, the latest in a string of military victories over the rebels since a major offensive was launched on October 25.
A senior official said Congolese troops had "completely conquered" the Mbuzi hilltop, as fighting raged in the mountainous region where rebels have retreated to since being forced from their last stronghold of Bunagana last week.
The latest clashes came despite a ceasefire call by M23 leader Bertrand Bisimwa on Sunday, which prompted international calls for Kinshasa to stop pressing on with the offensive.
Urging rebels to "immediately end hostilities", Bisimwa said his aim was to "allow the continuation of the political process" with Kinshasa in a bid to end the insurgency plaguing the long-troubled region since April 2012.
But the fighting only appeared to intensify after the M23 leader's appeal, with AFP journalists reporting that heavy shelling could be heard Monday in the small town of Ntamugenga near the battle zone in the lush, hilly region bordering Uganda.
"Victory, Victory," soldiers cried at a post in the town after receiving a radio message that their colleagues had taken Mbuzi.
Thousands flee into Uganda
The governor of the DR Congo's eastern North Kivu province, Julien Paluku, said shelling had left six people dead in Bunagana, a town on the border with Uganda.
Ugandan army colonel Paddy Ankunda said some shells had landed on its territory but there were no injuries or plans for any military response from Kampala.
The UN refugee agency meanwhile said it had moved another 3,000 Congolese refugees to its transit camp in Kisoro to escape the fighting, bringing the total number of refugees in the small Ugandan town to 8,000.
African leaders met in Pretoria in South Africa late on Monday to discuss the possibility of reinforcing the offensive UN brigade in the country.
Addressing the gathering, South African President Jacob Zuma urged leaders from the 15-country Southern Africa Development Community (SADC) and several of Congo's neighbours "to respond to the urgent challenges of restoring peace and stability".
The heavily-armed 3,000-strong UN intervention brigade joined 17,000 peacekeepers already deployed with a mission to carry out offensive operations against the rebel fighters, who are accused of human rights abuses including rape, murder and recruiting child soldiers.
In a joint statement issued early Monday, envoys from the European Union, African Union and the United Nations said they were "concerned about the renewed outbreak of violence" that followed the M23 truce call.
Analysts say better preparation by the Congolese troops and the backing of the UN brigade with the unprecedented offensive mandate have helped changed the game in the restive east of the DR Congo.
The M23 movement was founded by ethnic Tutsi former rebels who were incorporated into the Congolese army under a 2009 peace deal but mutinied in April 2012, claiming the pact had never been fully implemented.