Twenty armed men blocked a road and tried to hijack a convoy of food for earthquake victims, but were driven off by police gunfire, U.N. officials said Tuesday as they warned of security problems in a still-desperate nation.

The attack on the convoy as it carried supplies from an airport in the southern town of Jeremie underscored the shaky safety in the streets that has added to Haitians' frustration at the slow pace of aid since the Jan. 12 earthquake.

Most quake victims are still living outside in squalid tents of sheets and sticks and aid officials acknowledge they have not yet gotten food to the majority of those in need. Mobs have stolen food and looted goods from their neighbors in the camps, prompting many to band together or stay awake at night to prevent raids.

About 20 armed men blockaded a street Saturday and attacked a convoy carrying food from the airport in Jeremie, according to UN spokesman Vicenzo Pugliese. U.N. and Haitian officers fired warning gunshots and the men fled the scene, Pugliese said. No injuries were reported and no one was hurt.

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 in a statement Tuesday.

In Jacmel, also a southern city, 33 escaped prisoners were apprehended Sunday, the U.N. said. Many prisoners escaped 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.

About 40 protesters gathered outside the Haitian government's temporary headquarters, holding placards to demand pay for state workers. Many who had jobs before the earthquake can't return to work because buildings have collapsed.

Hundreds more waited outside the migration agency Tuesday to renew their passports in the hope they can leave the country. Others, despairing of government help, paid men to excavate loved ones from the rubble.

Hundreds gathered Monday 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 organized political rallies since the disaster.

Many denounced President Rene Preval and called for the return of ousted President Jean-Bertrand Aristide.

"Preval has done nothing for this country, nothing for the victims," said Jean Delcius, 54, who was bused to the memorial service by Aristide's development foundation. "We need someone new to take charge here. If it's not Aristide, then someone competent."

Critics were already blaming 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.

Preval has rarely been seen in public since, leaving Prime Minister Max Bellerive to defend the government's performance Tuesday as Haiti's Senate met in a prefabricated room at the police academy because its own building collapsed in the quake.

"Even the most advanced countries could not respond to this crisis," Bellerive said. "There is still a government, but we have no buildings. We have no equipment. We have no resources."

The government has asked all non-governmental aid groups in the country to start working with it to improve the often disjointed food distribution.

"It is true we are in need," said Sen. Jean Joel Joseph. "But don't treat us like dogs ... as if we are animals. We ask the prime minister to ask the foreigners to reorganize the way this aid is being distributed. "

Haiti's government also has had to deal with the 10 Americans who tried to take a busload of undocumented Haitian children out of the country.

The Idaho-based church group was being held without charges at a police station, where a judge met with them and a lawyer on Tuesday, said Communications Minister Marie-Laurence Jocelyn Lassegue.

Bellerive has said they could be prosecuted in the United States because Haiti's shattered court system may not be able to cope with a trial. U.S. Embassy officials would not say if a U.S. court process is possible.

At SOS Children's Village orphanage where authorities were protecting the 33 children found with the Americans, regional director Patricia Vargas said so far workers had not found any who said they were actually orphans. Parents apparently handed some over to clergyman accompanying the church group in hope they would have a better life.

Elsewhere, discontent with Preval appeared to be growing, three weeks after the disaster.

Aristide, a former slum priest had a huge following among Haiti's poor, but he was ousted in 2004 as corruption and drug trafficking grew rampant. He 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.

Before legislative elections scheduled for Feb. 28 were postponed, Haiti's presidentially appointed electoral council had excluded more than a dozen political parties _ including Aristide's _ from the next round of elections in 2011. Opposition groups accused the council of trying to help Preval expand his power.

Across the capital, Haitians have voiced anger over the hasty burials of earthquake victims.

Many Haitians believe that bodies must be properly buried and remembered by relatives and family so their spirits can pass on to heaven. In Voodoo, some believe that improper burials can trap spirits between two worlds.

The mourners on Monday gathered near a white metal cross erected on a mound of gravel that covered nameless bodies dropped into a pit by dump trucks. The corpse of a woman lay uncovered at the base of a nearby gravel pile.

One by one, people tied black pieces of cloth to the cross as a Catholic priest sprinkled the ground with holy water. A choir sang traditional Haitian hymns as religious leaders prayed for the dead.

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Associated Press Writers Frank Jordans contributed to this report from Geneva.