Heavy artillery fire and explosions shook central Abidjan Saturday on the third day of a fierce battle for the city, as rival forces were accused of massacring hundreds in western Ivory Coast.
Cornered, but clinging on, strongman Laurent Gbagbo brushed off calls by world leaders to step down amid an offensive by troops backing the internationally recognised president Alassane Ouattara in Abidjan.
Reports of carnage and massive displacement meanwhile emerged from the western town of Duekoue where the International Red Cross said 800 died in one day in an incident "particularly shocking by its size and brutality".
The Catholic mission Caritas reported 1,000 were "killed or disappeared" while the UN mission gave an initial death toll of 330, accusing fighters from both camps of involvement in the mass killings.
In Abidjan, an offensive by Ouattara's army on Gbagbo's strongholds continued, and walls shook as mortar and other heavy arms fire broke out in the afternoon near the presidential palace, AFP journalists said.
The UN mission UNOCI reported two separate attacks on its peacekeepers by Gbagbo forces, leaving four seriously injured, and warned its mandate allowed "the use of force when under attack."
While Gbagbo's camp claimed to have pushed back an assault Friday, Ouattara's fighters warned that the offensive "has not yet begun".
"We are taking steps to weaken the enemy before mounting an assault," said Captain Leon Kouakou Alla, spokesman for Ouattara's defence ministry.
Weary with failed diplomatic efforts to resolve a post-election crisis, Ouattara's army on Monday launched a lightning offensive across the country before arriving in Abidjan on Thursday.
Fierce fighting accompanied by loud explosions and bursts of machine-gun fire have sent residents of the city of five million people into lockdown, and more than 1,500 foreigners sought refuge at a French military camp.
As the violence escalated in the world's top cocoa producer, both camps have been accused of atrocities that rights groups say may amount to crimes against humanity.
Hundreds of bodies were discovered in the wake of a fierce battle for the town of Duekoue in the west, with accusations flying as to who is responsible.
"330 people (were) killed between Monday and Wednesday... the majority ... executed by 'dozos'," said Guillaume N'gefa of the UNOCI human rights division, referring to traditional hunters fighting with Ouattara's camp.
He said that among these more than a hundred were also killed by pro-Gbagbo forces.
A spokesman for the pro-Ouattara Republican Forces, Seydou Ouattara, said they had killed "militia and not civilians" and sought to distance the forces from the "dozos".
"Militiamen are not civilians. From the moment they are armed, they are considered combatants. We must avoid all confusion," he told AFP.
"The 'dozos' are a caste of hunters who have plantations in the west. They are also civilians who took up arms to defend their community. They are not members of the Republican Forces, but sympathisers," he said.
Ouattara's government accused "the loyal forces, mercenaries and militias of Laurent Gbagbo" of being behind mass graves discovered in the area.
A spokeswoman for the International Committee of the Red Cross (ICRC) in Geneva, Dorothea Krimitsas, told AFP information gathered by Red Cross workers showed "at least 800 people were killed in Duekoue on Tuesday" in what appeared to be inter-ethnic violence.
"There is no doubt that something on a large scale took place in this city," she said, adding that Red Cross workers had "themselves seen a very large number of bodies".
French President Nicolas Sarkozy's office condemned the "grave violence".
"Too many attacks, too many crimes have already been committed in Ivory Coast over the last four months. Those who are guilty of human rights abuses should know that they will be held to account," it said.
Several hundred people have been killed in the aftermath of the presidential election in November, and the UN estimates a million people have fled Abidjan in recent weeks fearing a bloodbath.
Former colonial master France, which has 12,200 nationals in Ivory Coast, has previously urged Gbagbo to quit power, as have the United States, the European Union, the African Union and the United Nations.