By Mark Doyle
BBC World Affairs correspondent
Negotiations have begun which could make or break the peace agreement signed last week with the key rebel leader in the Democratic Republic of Congo, General Laurent Nkunda, and the government.
At issue is whether another rebel group opposed to Gen Nkunda will also disarm.
A disarmament deadline - possibly in March - has been set for this second rebel group to disband, and if it is not met, military action has been promised.
In other words, paradoxically, more war has been threatened as a possible way of making last week's peace agreement with Gen Nkunda stick.
The thousands of displaced hope to return home to their villages
Some of the key individuals involved in the negotiations include the leaders of DR Congo and Rwanda, Joseph Kabila and Paul Kagame respectively, the US peace envoy to the region Tim Shortley, the British head of the UN mission to DR Congo, Alan Doss, and various armed militias.
The stakes are high; if the negotiations succeed they could end the sometimes proxy - and sometimes open - warfare that has pitted Rwanda and DR Congo against each other for a decade and a half.
This matters not only for humanitarian reasons - the conflicts in eastern DR Congo have made around a million people homeless in recent years - but for strategic ones too: DR Congo has a treasure trove of minerals sought by both the West and Asia.
The peace agreement signed with Gen Nkunda's group was described as "the best chance Congo has had for years" by lobby group Human Rights Watch.
The senior eastern Congolese politician, Azarias Ruberwa, also spoke optimistically.
In an exclusive BBC interview, Mr Ruberwa compared the deal to "the foundations of a house" that still has work to be done on it - but which represented "an important step in the process".
The agreement signed by Gen Nkunda's representatives included an immediate ceasefire and provision for buffer forces from the UN mission to deploy in sensitive areas.
Gen Nkunda was also offered what participants at the talks called "a partial amnesty".
All peace agreements in DR Congo have been difficult to police - partly because of the logistical difficulty of monitoring them in a country with poor infrastructure.
The delegates to the signing ceremony last week therefore expect some violations.
But the deal may face a more fundamental difficulty. It depends on another, parallel, agreement to disarm a second rebel group based in eastern DR Congo, the ethnic Hutu Democratic Front for the Liberation of Rwanda (FDLR).
The FDLR grew out of neighbouring Rwanda's ethnic Hutu forces which committed the genocide of Tutsis and moderate Hutus inside Rwanda in 1994.
These forces were then defeated militarily in Rwanda by the Tutsi-dominated Rwandan Patriotic Front led by Mr Kagame, and they retreated across the border into DR Congo.
Gen Nkunda has made it clear that the ultimate disarming of his Tutsi group will depend on guarantees that the Hutu FDLR is disbanded.
"The Rwandan Hutu rebels have in part been dealt with by an accord signed between the governments of Congo and Rwanda last November," explains Anneke Van Woudenberg of Human Rights Watch from Goma.
"Both agreed they would take action against the group. The Congolese government said they would tell them they were no longer welcome, and if they didn't go home by March, then they would start military operations against them."
Mr Ruberwa, a Tutsi, says the situation is clear: "Under the calendar, they are supposed to go home. If some refuse then another step will be taken - force."
A business affair
Congolese foreign ministry officials are reported to have already made direct contacts with the FDLR in the forests of eastern DR Congo, following the Nkunda peace agreement.
Gen Nkunda was offered a partial amnesty
The details of the contacts were secret but it seems likely that the possible March deadline for an FDLR departure was discussed.
Force may be necessary, diplomats in the region say, because the Hutu militia are understandably suspicious of the Tutsi-dominated government in Rwanda.
To the extent that individuals within the FDLR took part in the 1994 genocide of Tutsis and still represent a threat, the government in Kigali would like to see them neutralised - behind bars or otherwise.
And some members of the Hutu militia do still harbour a desire to overthrow President Kagame, who they accuse of oppressing Hutus.
"The Hutu militia has to leave Congo," say Congolese political analyst Muzong Kodi, currently working with the Royal Institute of International Affairs in London.
He feels the FDLR "are a menace to the Congolese population".
"The Rwandan government should hand over a list of those among them involved in the genocide; they should face the courts," he says.
"Those who were not involved should be allowed to return to Rwanda and not be persecuted."
But Mr Kodi dismissed allegations by Rwanda that the FDLR were a real threat to the Kigali government.
"That's just a pretext. The Rwandan army was in Congo from 1996 until 2003, and they didn't deal with the FDLR then," he said.
Instead, he says, Rwandan businessmen used their army's presence as a way of protecting new and sometimes illicit business affairs in eastern DR Congo.