The M23 rebel group has threatened to pull out of peace talks with the Democratic Republic of Congo government unless President Joseph Kabila signs a ceasefire agreement.
Talks are due to start in the Ugandan capital, Kampala, on Friday.
A Congo government spokesman told the Reuters news agency it rejected a rebel demand he described as “pointless”.
A first attempt to negotiate an end to the nine-month rebellion in the east of the country failed last month.
As many as 800,000 people have been displaced since the rebels took up arms against the Kinshasa government last May, accusing it of failing to honour an earlier peace deal to integrate rebels into the army.
The rebels, led by Bosco Ntaganda who is wanted by the International Criminal Court on war crimes charges, made rapid gains late last year.
They seized the main city in the region, Goma, in November, but withdrew under international pressure.
The head of their political wing, Jean-Marie Runiga, told journalists on Thursday the government had not matched his group’s offer of a ceasefire and had been reinforcing its positions.
“If Kinshasa continues to refuse to sign a ceasefire, M23 is going to ask its delegation to return to DRC,” Mr Runiga said.
Joseph Kabila has little control over eastern Congo
“We will wait and when they say: ‘We’re ready to sign’, we’ll go back.”
M23 say they want to improve living conditions for the people of eastern DR Congo, but the UN say they are supported by Rwanda, which has been heavily involved in its eastern neighbour since those responsible for the country’s genocide fled there en masse in 1994.
Bosco Ntaganda, who set up M23, was an officer in the Rwandan army before he left to join a rebel movement in DR Congo. The ICC accuses him of using child soldiers and the UN says he controls several mines in the east of the country.
The government in Kinshasa has had little control over the east since the overthrow of Mobutu Sese Seko in 1997. The region’s mineral riches have been plundered by numerous groups and countries over the past 15 years and little has been spent on DR Congo’s infrastructure.
President Kabila easily won re-election in 2011 in a vote described by international observers as “lacking credibility”.
But he scored poorly in the east of the country and the M23 rebels refuse to accept the legitimacy of his re-election.