Soldiers backing Ivory Coast's defiant leader mowed down women protesting his refusal to leave power in a hail of gunfire Thursday, killing at least six and shocking a nation where women's marches have historically been used as a last resort against an unrestrained army.

Because the president's security force has shown almost no reserve in opening fire on unarmed civilians, the women decided this week to organize the march in the nation's commercial capital Abidjan, assuming soldiers would be too ashamed to open fire.

But at least six of the thousands of women demonstrating Thursday were killed on the spot, said Mohamed Dosso, an assistant to the mayor of Abobo, a suburb of the city.

The three-month old conflict in Ivory Coast has entered a new level of intensity. With each passing day, the regime of Laurent Gbagbo is proving it is willing to go to any length to stay in office following an election that international observers say he lost.

Sirah Drane, 41, who helped organize the march, said she was holding the megaphone and preparing to address the large crowd that had gathered at a traffic circle in Abobo.

"That's when we saw the tanks," she said. "There were thousands of women. And we said to ourselves, 'They won't shoot at women.'…I heard a boom. They started spraying us…I tried to run and fell down. The others trampled me. Opening fire on unarmed women? It's inconceivable."

Attack prompts U.S. rebuke

The attack prompted an immediate rebuke from the U.S., which like most governments has urged Gbagbo to step down and has recognized his rival as the country's legitimate president.

"The moral bankruptcy of Laurent Gbagbo is evident as his security forces killed women protesters," said U.S. State Department spokesman P.J. Crowley in a Twitter message.

In New York, the UN Security Council said it is "deeply concerned" about the escalation of violence in Ivory Coast and that it could lead to a resurgence of civil war there.

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Residents flee with their belongings after clashes between forces loyal to incumbent president Laurent Gbagbo and his rival Alassane Ouattara in Abidjan last month. (Luc Gnago/Reuters)

Nearly 400 people have been killed in the west African country, including 32 in the last 24 hours, almost all of them men who had voted for opposition leader Alassane Ouattara, according to UN figures and combined with deaths confirmed by The Associated Press.

Last week, Gbagbo's security forces entered the Abobo neighborhood and began shelling it with mortars, a shocking escalation indicating the army is willing to use war-grade weapons on its citizens. Before that, the bodies seen by reporters had bullet wounds where the point of impact was marked by a single stain of blood. Since the escalation, the bodies seen by reporters have arrived at the morgue in body bags dripping with blood.

A 14-year-old's corpse had hundreds of shrapnel wounds across the chest, and the doctor who attempted to save him last week said the wounds were the result of a fragmentation grenade, similar to those used in Iraq and Afghanistan.

In Abobo, the official in the mayor's office said that one of the women had been "torn to pieces" by the barrage of gunfire.

"A woman," Dosso said in disbelief.

For days, families carrying suitcases streamed out of the district in a massive exodus. At least 200,000 people have fled the suburb, said Guillaume Nguefa of the human rights division of the UN mission in Ivory Coast.

"In Abobo district, the government is using heavy artillery weapons against people," he said.

Multiple delegations of African leaders have come through Abidjan to try to persuade Gbagbo to leave office. Gbagbo has rejected all their proposals and offers of amnesty, including the U.S.'s offer of a professorship at a Boston university.

Gbagbo, a former history teacher, has refused to cede power, even though UN-certified results showed he had lost the race by half-a-million votes to Ouattara. Instead, he demanded the UN leave the country and accused them of meddling in state affairs.