Congolese rebels have threatened to walk away from this week's peace talks to end their nine-month revolt unless the government signs an official ceasefire, a demand Kinshasa dismissed as unnecessary.
The rebel March 23 Movement, preparing for talks on Friday in Kampala, capital of regional mediator Uganda, said government troops had reinforced positions in the east of Democratic Republic of Congo (DRC) and warned it would resist an offensive.
"If Kinshasa continues to refuse to sign a ceasefire, M23 is going to ask its delegation to return to DRC. We will wait and when they say 'we're ready to sign [a ceasefire]' we'll go back," Jean-Marie Runiga, head of the rebels' political wing, told reporters in Bunagana, a border town under rebel control.
The first attempt at peace talks to end the nine-month rebellion in Congo's volatile east failed last month amid threats and accusations. A government spokesman dismissed the rebel demand.
"There's no point in a ceasefire. When did we declare war?" Lambert Mende told the Reuters news agency by telephone.
"This group wants permission to kill Congolese without the army reacting, and we will never accept that. If they attack us, attack the people, the army will defend the people."
Negotiations began last month after regional leaders secured a rebel pull-out from the city of Goma in Congo's eastern North Kivu province.
The front lines have been quiet since, although the talks quickly stalled in a climate of deep mistrust.
Foreign powers fear the conflict could spark another regional war in a borderlands zone that has suffered nearly two decades of turmoil.
Neighbouring Uganda and Rwanda are accused by a group of UN experts of supporting the rebel campaign.
Successive cross-border conflicts have killed and uprooted millions in the Congo basin since the colonial era, driven by political and ethnic divisions and competition for minerals.
At first, M23, named after a 2009 peace deal for eastern Congo, said it had taken up arms because the Kinshasa government failed to honour its side of the bargain, under which rebel fighters were integrated into the army.
It later broadened its goals to include the "liberation" of all of Congo and the removal of President Joseph Kabila.
M23 is led by Bosco Ntaganda, a Tutsi warlord indicted by the International Criminal Court. This week the United Nations blacklisted M23 along with another Congolese rebel group.
"We need encouragement from the UN, not sanctions," Runiga, flanked by fighters, said.
Nestled in lush green hills less than a kilometre from the Ugandan frontier, Bunagana fell into rebel hands last July after government soldiers fled.
The other group hit with UN sanctions was the FDLR, or Democratic Forces for the Liberation of Rwanda. The FDLR is a Rwandan Hutu group that opposes Rwandan President Paul Kagame's Tutsi-led government and includes militiamen suspected of participating in Rwanda's 1994 genocide.
One M23 commander, Bertrand Bisimwa, said Congo's government had air-dropped FDLR fighters to reinforce army positions near Goma last month. Officials from the government were not immediately available to comment on the accusation.