A much anticipated peace deal between the Democratic Republic of Congo (DRC) and the M23 rebel militia has fallen through after the government demanded changes to the agreement in the final stages of talks in Kampala, Uganda.

Both sides remain in Kampala and the talks are yet to be officially called off, according to a spokesperson of the Ugandan government.

Monday’s presumed peace deal was expected to cap a fortnight of frenetic activity in which M23 called off its 20-month rebellion in the DRC’s conflict-prone eastern provinces after a decisive military campaign by security forces.

The current standoff has tempered some of that early optimism.

A joint statement issued by the African Union and the European Union said “the parties have expressed no differences on substantive points within the draft document.” However, M 23’s disavowal of violence could have led the DRC government to push for concessions believing it had the upper hand in negotiations.

The U.N. Secretary-General’s Special Envoy to the Great Lakes Region, Mary Robinson, and the United States Special Envoy, Russ Feingold, said, “Any solution must allow the pursuit of accountability for those who have committed war crimes, crimes of genocide, [and] crimes against humanity.”

The M23 militia draws its name from a March 23, 2009 peace deal that promised to integrate soldiers from a prior rebellion in eastern Congo that stemmed from an ethnic conflict sparked by the Rwandan genocide of 1994.

In April last year, former rebels restarted their rebellion, accusing the government in Kinshasa of disregarding the March 23 agreement.

Since then, U.N. reports have accused Rwanda of using M23 to foment unrest in DRC by training, arming, and commanding M23 rebels and providing fighters safe haven. Uganda was accused of providing M23 with political support.

Both countries have denied the allegations, but the United States, the European Union and Britain responded by cutting aid to Rwanda to force Kigali to rein in the rebels.