The Democratic Republic of the Congo's M23 rebel movement appeared to be starting to withdraw from the eastern city of Goma after defying a deadline set by regional leaders, a U.N. official said Tuesday.

"There were indications tonight that possibly the M23 elements were starting to withdraw," Herve Ladsous, the U.N. peacekeeping chief, told reporters at the world body's headquarters in New York. "There were indications, but of course that was already late the evening, and that will have to be confirmed tomorrow."

The rebels seized control of Goma, a key city in eastern Congo, last week and ignored a call by the leaders of the African Union and neighboring states to pull out by midnight Monday. M23 political leader Jean-Marie Runiga told reporters in Goma on Tuesday that the rebels would hold their ground until negotiations start with the Congolese government and their conditions are met.

Both rebel and government troops were massing west of Goma, setting the scene for possible future clashes. But Ladsous said the M23 appeared to be starting its withdrawal and was not advancing elsewhere.

The group was named for a peace deal reached on March 23, 2009, which it accuses the government of violating. Its demands include the release of political prisoners, the investigation of alleged targeted killings in the country, the dismissal of the national election commission and the examination of the results of last year's election.

African leaders who convened in neighboring Uganda over the weekend released a statement demanding that the M23 group withdraw at least 20 kilometers (12 miles) north of Goma as a condition of initiating negotiations. The Great Lakes region leaders called on the rebels to "stop all war activities," and "stop talk of overthrowing an elected government."

Congo Information Minister Lambert Mende Omalanga, in Kinshasa, described the M23 response as "really childish."

"We think these people are not taking this seriously, which makes them very dangerous," Omalanga told CNN. He said the rebels' objectives are unclear and, as a result, he doubts they have any intention to negotiate because "they don't know what they want."

He accused the rebels of being "busy looting Goma," adding that they have pillaged public buildings and hospitals and tried to break into a bank.

Congolese army spokesman Col. Olivier Hamuli said the armed forces were awaiting guidance from the government and would abide by a cease-fire until they were told to do otherwise.

Speaking Tuesday, Runiga said that the rebels want to sit down and discuss the March 23 agreement with civil society, the government and a broad spectrum of the Congolese people to come up with lasting solutions on good governance, democracy, the economy and security.

He also said an investigation should be undertaken into the distribution of weapons in eastern Congo and "foreign" armed groups working in Congo -- such as the Lord's Resistance Army and the FDLR, a Hutu-dominated Congolese group -- should be defeated.

Runiga claimed that the FDLR tried to attack Rwanda on Tuesday, but members of M23 arrested its fighters. Comment from the Rwandese government was not immediately available.

Runiga also said the M23 would maintain a humanitarian corridor and called on people to respect the role of MONUSCO, the U.N. peacekeeping force in the region mandated to protect civilians.

He asked people to respect the U.N. peacekeepers' presence in Goma and not to throw rocks at passing patrols.

MONUSCO forces took a back seat as army forces battled the rebels for control of the city last week.

Runiga also warned that if President Joseph Kabila and his government do not want to negotiate, the rebels will push on to South Kivu and the capital, Kinshasa, where they will overthrow the government by force. The M23 group has made similar threats in the past.

Omalanga, the information minister, said the Congolese government is evaluating the effectiveness of MONUSCO in light of the peacekeepers' response to the rebels' seizure of Goma.

The government is not jumping to conclusions, Omalanga said, but he added: "They don't have an appropriate mandate -- this must absolutely change if the U.N. wants it to be effective in Congo."

Meanwhile, in the Ugandan capital, Kampala, Gen. Aronda Nyakairima set out details of the plan agreed by the Great Lakes region leaders at the weekend.