Updated

Assailants in a pro-opposition neighborhood ambushed and killed at least 20 security forces loyal to the sitting president — an attack which is likely to escalate violence in the region.

Officials said Wednesday that the deaths occurred in a neighborhood of the district of Abobo. The neighborhood, PK-18 , has been the subject of a brutal crackdown by troops allied with Ivorian leader Laurent Gbagbo, who has refused to accept defeat in last year's presidential election.

Dozens of civilians that voted for Gbagbo's challenger Alassane Ouattara have been killed in PK-18. An untold number have been 'disappeared' and some of their bodies have been found by families in morgues that are so full they are turning into mass graves.

But on Tuesday, PK-18 fought back. The military convoy that attempted to enter the neighborhood was attacked, and four pickup trucks were seized. At least 20 soldiers and police were killed, said Capt. Leon Kouakou Alla, a military spokesman for Ouattara.

Residents described hours of heavy machine gunfire and grenade explosions Tuesday.

"It was a nightmare," said the resident, who spoke on condition of anonymity for fear of retribution. "There were explosions and the deafening sound of machine guns. This wasn't the little pops of Kalashnikovs — we're used to that," he said.

While Alla put the death toll at 20, an official inside Ouattara's cabinet who asked not to be named because of the sensitivity of the matter said it was as high as 30, including policemen and members of the paramilitary CECOS unit.

The death toll could not be independently verified, but if either is correct it suggests the civilian area has been infiltrated by commandos allied with Ouattara.

"We don't know exactly how many FDS (pro-Gbagbo security forces) were killed. But four FDS trucks were seized. Each of these vehicles is capable of carrying between 6 and 10 people. They were all eliminated. You do the math," said Alla.

Last week, Ouattara's prime minister warned that if Gbagbo refuses to stand down, supporters of Ouattara will rise up in an "Egypt-style" revolution. He said they will be helped by the country's northern rebels, who are politically aligned with Ouattara.

The United Nations, Amnesty International and Human Rights Watch have condemned the human rights abuses, which include executions, kidnappings and rape, carried out by pro-Gbagbo security forces against supporters of Ouattara.

An investigation by The Associated Press showed at least 113 bodies are being held in Abidjan's morgues by officials who wouldn't release them for burial.

Officials in Gbagbo's government say armed rebels have infiltrated the population in Abobo and have been firing on police. Members of the New Forces rebels refuse to comment on the issue, but stories of the "invisible commandos" circulate freely in Abidjan.

Late on Wednesday, residents of Abobo reported that security forces had returned en masse. Several said they saw half a dozen trucks filled with riot police and paramilitary units. Shooting could be heard.

A number of people said the shooting sounded like heavy artillery, not just small arms fire.

On the Wednesday afternoon news, a military spokesman for the Gbagbo regime described the Tuesday incident as an "ambush by a group of more than fifty rebels."

"Under a deluge of fire, the (police) returned fire courageously," he said in a statement read on state television which is controlled by Gbagbo.

He put the death toll at nine, but said only two of them were security forces.

Ouattara is considered the legitimate president of Ivory Coast by governments around the world, but he has not been able to assume office because Gbagbo is refusing to leave. On Tuesday, a high-level delegation sent by the African Union was in Abidjan to meet with the warring sides in an attempt to find a solution. They left Wednesday having made no progress.

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Associated Press Writer Rukmini Callimachi contributed to this report from Dakar, Senegal.