The UN warned today that Haiti was sinking into potential violent chaos as people grow frustrated at the slow pace of aid getting through.
Most victims are still living outside in squalid tents of sheets and sticks and aid officials acknowledge they have not yet got food to most of those in need.
Mobs have stolen food and looted goods from their neighbours in the camps, prompting many to band together or stay awake at night to prevent raids.
About 20 armed men blockaded a street on Saturday and attacked a convoy carrying food from the airport in Jeremie. UN and Haitian officers fired warning gunshots and the men fled.
Haitian police have increased their own patrols and are accompanying UN police guarding aid distribution.
"The overall security situation across the country remains stable but potentially volatile," the UN mission said today.
In Jacmel, also a southern city, 33 prisoners on the run were caught on Sunday, the UN said after mass escapes when prisons collapsed.
While Haitians are still mourning friends and relatives, many still unburied, anger at the government's sluggish response to the quake is feeding political resentment.
Hundreds gathered yesterday at a gravel pit in Titanyen where countless earthquake victims have been dumped, turning a remembrance ceremony for the dead into one of the first organised political rallies since the disaster.
Many denounced President Rene Preval and called for the return of ousted President Jean-Bertrand Aristide.
Critics were already blaming Mr Preval for rising unemployment, corruption and greed. Then the earthquake struck, flattening most government buildings and turning the capital into an apocalyptic vision of broken concrete and twisted steel.
He has rarely been seen in public since, leaving his ministers to defend his performance and discontent with him appears to be growing, three weeks after the disaster.
Mr Aristide also faced criticism during his presidency. The former slum priest had a huge grassroots following among Haiti's poor but was overthrown in 2004 as corruption and drug trafficking grew rampant and some of former supporters accused him of abandoning his early followers to line his own pockets.
Mr Aristide has said that he would like to return from his exile in South Africa - a move that would add political instability to the post-quake chaos and likely face resistance from the international community.
Before elections scheduled for February 28 were postponed, Haiti's presidentially appointed electoral council had excluded more than a dozen political parties from the next round of elections in 2011.
Opposition groups accused the council of trying to help Mr Preval's Unity party win majorities in parliament so he could push through constitutional reforms and expand executive power.