A meeting of regional heads of state seeking a lasting solution to chronic unrest in the east of the Democratic Republic of Congo will not start before Saturday, officials said.
The mini-summit had been scheduled to start Friday but officials said regional defence ministers have not yet agreed on the proposals to be discussed.
Eastern DR Congo has been hit hard by a new rebellion by army defectors who formed a group called the M23, whose members are former fighters in an ethnic Tutsi rebel movement integrated into the military under a 2009 peace deal.
"While there has been a lull in military activities by the M23 in North Kivu since July, the situation remains very fragile," the top United Nations' official for central Africa, Abou Moussa, said in a message ahead of the summit.
"I call for the group's immediate and complete cessation of all destabilising activities," he added.
A UN report in June accused Rwanda of backing the rebels, causing a surge in tensions with neighbouring DR Congo. Kigali denies the charge, and has been in talks with Kinshasa to set up a "neutral force" to tackle the unrest.
The latest meeting, hosted by Ugandan President Yoweri Museveni, will consider recommendations drawn up by a panel of regional defence ministers at a meeting in mid-August in the eastern DRC town of Goma.
DR Congo President Joseph Kabila is in Kampala for the summit but his Rwandan counterpart Paul Kagame will be represented by his defence and foreign ministers. Tanzanian President Jakaya Kikwete is also in attendance.
Museveni hosted regional leaders in early August, who agreed that a sub-committee of seven defence ministers led by Uganda should be put in place to help Kinshasha restore peace and security in eastern DR Congo.
The team comprises ministers from Angola, Burundi, Congo, DR Congo, Rwanda, Uganda and Tanzania, seven of the 11 member nations of the International Conference on the Great Lakes Region (ICGLR).
South Sudan is poised to join the grouping and the new country's president Salva Kiir is in Kampala for the meeting.
The ICGLR countries have been meeting at ministerial and heads of state level for the past two months. Analysts say the latest meeting is unlikely to make more progress than the last meeting in Kampala or a meeting in July in the Ethiopian capital Addis Ababa.
If anything, tensions between DR Congo and Rwanda may be running higher this time round.
The presence in DR Congo -- with the approval of President Joseph Kabila -- of Rwandan special forces, who were taking part in joint military operations with Congolese troops against a different rebel group and who were withdrawn last Friday by Kigali in a blaze of publicity, has further stoked tensions.
The country's main opposition party accused President Joseph Kabila of "high treason" over the presence of the Rwandans.
Even if the summit were to make concrete progress on M23 and relations between Kinshasa and Kigali, a plethora of other armed groups also operate in eastern DR Congo, a region that has been in turmoil for the best part of the past two decades.
Much of the rebel activity in the region consists of abuses against civilians and illegal exploitation of natural resources, be it metals, ivory or timber.
Fighting in the region has displaced more than 220,000 people since April, and more than 57,000 others have fled to Rwanda and Uganda.
"I once again condemn the violence and serious human rights violations committed by the M23, as well as other armed groups, against civilians, which need to be thoroughly investigated by relevant institutions and the perpetrators held accountable," Abou Moussa said in his message.
Several other armed groups also operate in the region.