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.