At least 800 people have been reported killed in one town in Cote d'Ivoire, according to the Red Cross, as fierce fighting continues to grip the country.
The International Committee of the Red Cross (ICRC) said the deaths reportedly took place during intercommunal violence in the western town of Duekoue on Tuesday.
Dorothea Krimitas, an ICRC spokeswoman, said on Saturday that the violence likely erupted the day after the town was taken by fighters loyal to Alassane Ouattara, the country's internationally recognised leader.
"This event is particularly shocking because of the magnitude and because of the extent of its brutality," Krimitas told Al Jazeera.
"We strongly condemn direct attacks against civilians and we would also like to take this opportunity to recall the obligations of all parties to the conflict to ensure in all circumstances the protection of the population on the territory they are controlling."
It was not clear what prompted the killings and whether the fighters were involved but Krimitas said that the death toll may rise as investigations on the ground continue.
"Our colleagues have been on the field over the past two days, collecting more information and hopefully we will be able to gain a clear picture soon ... they have seen hundreds of bodies ... they have been able to evacuate 28 bodies to the morgue [so far] but activities should be ongoing in the coming days," she said.
The statement came as forces loyal to Ouattara encircled the residence of Laurent Gbagbo, the country's incumbent president, as the fierce standoff between the two sides continued.
On Thursday, pro-Ouattara forces marched into the country's largest city, They intend to battle Gbagbo's forces in their stronghold, Kouakou Leon Alla, a spokesperson for the defence minister and the prime minister, said.
"After the tremendous work throughout the interior of the country, the Republican Forces are reorganised to complete their noble mission," he said.
They will also be fighting to rid the city of the prisoners released and armed by Gbagbo. On Friday afternoon, two patrols of pro-Ouattara troops came under fire, in what Leon Alla condemned as a "war crime".
By the time the military vehicles crossed into Abidjan, as many as 50,000 members of Gbagbo's security forces had deserted, according to the top UN envoy in Cote d'Ivoire, Choi Young-jin.
Yet even in the face of a rapid military advance that has swept across the West African country and arrived at his doorstep in Abidjan, Gbagbo has rejected calls to step down.
And while Ouattara's supporters faced little initial resistance in their swift push south, they now face Gbagbo's most reliable fighters, the roughly 2,500-strong elite Republican Guard, clustered in Abidjan along with remaining regular army troops.
His aides defiantly said they will never give in, though nearly 80 per cent of the country and now large swaths of its largest city are reportedly controlled by an armed group fighting to install Ouattara.
"There is no question of ceding," said Gbagbo's presidential aide, Fred Anderson. "It's not up to the international community to impose our leader."
In the Cocody neighbourhood where the presidential mansion is located, families slept in bathrooms and on the floor as successive blasts punctuated an all-night assault, continuing into Saturday morning. Machine-gun fire could be heard at either end of the waterside highway leading to the palace.
In the Rivera neighbourhood armed members of the "young patriots," the youth wing of Gbagbo's camp, patrolled areas and organised checkpoints.
"At the cost of our blood, we are going to die so that the republic survives, for our children, because this is an unjust war," an armed young patriot, calling himself General La Poudriere or Minefield, said.
Military officials loyal to Ivory Coast's entrenched leader on Saturday called on their forces to resist rebels who are trying to depose him after he has refused to cede power.
Forces loyal to incumbent leader Laurent Gbagbo retook state TV headquarters on Saturday.
Gbagbo's military spokesman Lieutenant Colonel Alphonse Guano then made a televised address.
In it, he called on security forces to report for duty to resist attacks by forces loyal to internationally recognised president Alassane Ouattara, whose fighters now control most of the country.
Flanked by other soldiers, Guano said the state security forces were "being attacked by opportunistic forces including the United Nations, French forces and rebels.
He then claimed that "the actions of these forces include assassinations, killings and theft and unfortunately the victims have been innocent populations."
Ouattara's victory in November with 54 per cent of the vote was recognised first by the country's electoral commission and then by the United Nations, which pored over thousands of tally sheets before certifying the results.
He has also been recognised by governments around the world, and leaders from US president Barack Obama to French president Nicolas Sarkozy have made personal appeals to Gbagbo to step down.
"This turn of events is a direct consequence of the intransigence of the outgoing president, Mr Laurent Gbagbo, who has repeatedly refused to heed calls for him to cede the reins of power in the country to the president-elect, Mr Alassane Ouattara," said a statement on Friday from the regional Economic Community of West African States (ECOWAS).
Gbagbo, 65, has not been seen in public since the offensive began five days ago, but those in his inner circle say he is still in Abidjan and will fight until the end. It is unclear where he is holed up, with Ouattara's camp speculating he is in a bunker in the palace.
Reached by telephone, however, one of Gbagbo's closest associates, foreign minister Alcide Djeje, said he was at Gbagbo''s side at the presidential residence in Cocody.
Ouattara ordered land and sea borders closed to seal all the exits in case Gbagbo attempts to flee, said foreign affairs minister Jean-Marie Kacou-Gervais.
"His inner circle is trying to run, but they won't be able to," he said.
Members of Ouattara's administration said the battle would already be over if Ouattara had not given specific instructions to not harm Gbagbo.
"It is not our wish to kill him," Kacou-Gervais said. "We would like the Red Cross to be a witness. We invite them to be with us when we take him."
At least one million people have fled Abidjan and 494 have been killed during the four months of violence.
Meanwhile, UN deputy spokesman Farhan Haq said the UN High Commissioner for Human Rights has received "unconfirmed but worrying reports" that the pro-Ouattara force "has been committing human rights violations" during the advance toward Abidjan.
Secretary-General Ban Ki-moon again called on Gbagbo to step down and transfer power to Ouattara, telling reporters in Nairobi, Kenya, that "there has been too much bloodshed".
Since the disputed election, Ouattara had worked to rally international support for an armed intervention led by either the UN or a regional force to avoid the impression that he had taken the country by violent means.
Ouattara's aides said he exhausted all diplomatic options before giving the armed group the go-ahead.