Hundreds gathered Monday at a gravel pit 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, with followers denouncing President Rene Preval.

Many called for ousted President Jean-Bertrand 해적맞고 Aristide's return - a familiar political refrain when things swing between bad and worse in Haiti.

"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."

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One of the main challenges facing Haiti and the flood of international aid workers who came to the country after the earthquake has been security.

The United Nations said Tuesday the security situation in Haiti was now "stable but potentially volatile," even as the U.N.'s humanitarian office said an armed group attacked a food convoy at the Jeremie airport in the southwest of the country.

It said U.N. peacekeepers fired warning shots and there were no injuries. The global body said Haitian national police were stepping up patrols to prevent violence and apprehended 33 escaped prisoners on Saturday.

U.N. spokeswoman Elisabeth Byrs said Tuesday several hundred prisoners are still believed to be on the loose after their prisons collapsed in the Jan. 12 quake.

Even before the quake critics were blaming Preval for rising unemployment, corruption and greed. Then the Jan. 12 earthquake struck, killing at least 150,000 people, 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 his ministers to defend his performance - a job they are growing increasingly weary of.

Asked Monday about the criticism of Preval, Communications Minister Marie-Laurence Jocelin Lassegue batted back the questions, frowning and looking irritable.

"Those questions are for the president or the prime minister," he told The Associated Press.

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. Prime Minister Max Bellerive also told the AP that "what they were doing was wrong," and they could be prosecuted in the United States.

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"It is clear now that they were trying to cross the border without papers. It is clear now that some of the children have live parents," Bellerive said. "And it is clear now that they knew what they were doing was wrong."

U.S. Embassy officials would not say whether Washington would accept hosting judicial proceedings for the Americans. For now, the case remains firmly in Haitian hands, State Department spokesman P.J. Crowley said in Washington. "Once we know all the facts, we will determine what the appropriate course is, but the judgment is really up to the Haitian government," he said.

Meanwhile, discontent with Preval appears to be growing, three weeks after the disaster.

"He came Saturday and then just left," said Jude John Peter, 23, in a camp across from Haiti's demolished National Palace, where some 2,000 people are crammed into tents made of bedsheets and sticks, fighting for clean water and one portable toilet. "He's nowhere to be seen at first and then leaves when things get hot."

Aristide faced similar criticism during his presidency. The former slum priest had a huge grassroots following among Haiti's poor but was ousted in 2004 as corruption and drug trafficking grew rampant and some of his former supporters accused him of abandoning his early followers to line his own pockets.

Aristide has declared since the quake 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 legislative elections scheduled for Feb. 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 Preval's Unity party win majorities in parliament so he could push through constitutional reforms and expand executive power.

The most prominent excluded party is Aristide's former Lavalas party, which now plans more demonstrations. That will force thousands of American soldiers and U.N. peacekeepers to worry about containing political violence as well as providing relief.

"There are people trying to make political capital out of this very difficult moment," said Arnold Antonin, an environmental activist.

Some who attended the memorial said they simply wanted new leadership. Voter discontent is a constant in impoverished Haiti, where for years after the dictatorship, some even claimed they wanted the return of Jean-Claude Duvalier, whose father, Francois "Papa Doc" Duvalier, launched a 29-year family dynasty of terror.

"When there's a great deal of discontent among the population, people look at the government and start considering past demagogues," said James Morrell, director of the Washington, D.C.-based Haiti Democracy Project.

"This could explain people contemplating the return of Aristide," Morrell said. "But the question that Haitians are really asking is, what would the mechanism be to get capable Haitians into the country who could manage the situation?"

Tens of thousands were killed by the Duvaliers - many of them also buried anonymously in the gravel fields of Titanyen.

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.

"We've come here to bless these people, to bless this spot," said the Rev. Patrick Joseph Neptune.

Meanwhile, others in the crowd planned another political rally for Tuesday.

"If Preval comes, we will kill him!" they shouted.