Rising violence and a power vacuum caused by the ousting of Islamic forces by the transitional government could lead to a return of the chaos that plagued Somalia for 16 years, the U.N. said in a monthly report.
The spiraling violence is also likely to undermine attempts to deploy an African Union peacekeeping mission designed to protect the country's weak, Ethiopian-backed government and train a new army for the lawless nation.
"The re-emergence of warlords also raises serious concerns about the need to ensure principled humanitarian action and a do-no-harm approach," the U.N said. The report warned it was critical to avoid the "coercion and violence" perpetrated by warlords and their militias in the past, as they sought to cash in on aid flowing into the country.
The U.N. estimates around 1 million Somalis need humanitarian aid.
In Mogadishu, the nation's restive capital of 2 million, gunmen are being paid $2 a day to serve as vigilantes, according to businessmen and residents. Fighting here has killed at least 25 people in the last two weeks.
"The government has to take responsibility for security, before they get help from African peacekeepers," said Abdi Mo'ali Husein, a resident who has organized private security efforts.
About 15 private checkpoints have been set up in residential areas and armed militia are being employed by businesses to prevent attacks, according to Ibrahim Omar Sabriye, Mogadishu's deputy mayor.
Mogadishu Police Chief Ali Sa'id Abdi said his officers are working to contain the violence.
Islamic extremists opposed to the government routinely attack official buildings in Mogadishu, as well as Ethiopian troops deployed here.
In December, Ethiopia sent thousands of soldiers into Somalia to help the U.N.-recognized government defeat an Islamic movement trying to take over the country.
The AU peacekeeping force would replace the Ethiopian soldiers, who are widely despised by Mogadishu residents. However, it is not clear if the peacekeepers would be welcome, either, after demonstrations over the weekend by Somalis opposed to the expected AU deployment.
The U.N. Security Council is discussing in New York a draft resolution on Somalia, giving its blessing to an AU peacekeeping force that would serve in the country for six months.
Ethiopia had planned to withdraw its forces quickly, although the growing unrest makes a full withdrawal unlikely until at least the arrival of AU troops.
Ethiopian Foreign Affairs Minister Seyoum Mesfin met with Somali President Abdullahi Yusuf on Tuesday in the southern town of Baidoa.
They discussed the worsening security situation and resurgence of resistance groups, said a government official who declined to give his name because he was not authorized to talk to the media.
Somalia has not had an effective national government since 1991, when warlords overthrew dictator Mohamed Siad Barre and then turned on one another, throwing the country into anarchy. A transitional government was formed in 2004 with U.N. help, but has had little authority because it has no real army or police force.