Amnesty International has warned of a "human rights black hole" in Ivory Coast as at least six more protesters were killed in clashes on Monday.
Tensions have escalated since President Laurent Gbagbo has refused to hand over to Alassane Ouattara, widely recognised as the winner of November's poll.
The UK-based rights group says it has evidence of rape and extrajudicial killings being committed by both sides.
Four African presidents are in Abidjan to mediate an end to the crisis.
The BBC's Ivory Coat correspondent John James says it is the last diplomatic attempt to end the stalemate, which has brought the world's largest cocoa producer close to economic collapse.
Over the last week all the main commercial banks closed their doors, he says.
Business activity is now at a standstill, with few ships now calling at the two main ports after the European Union put them on a sanctions list.
The presidents of South Africa, Tanzania, Chad and Mauritania arrived on Monday during renewed protests in the main city of Abidjan.
Witnesses said soldiers from units loyal to President Gbagbo shot at supporters of Mr Ouattara, killing at least six people.
Burkina Faso's President Blaise Compaore, another member of the African Union panel, cancelled his trip after the pro-Gbagbo militia threatened to attack his convoy, alleging he supported Mr Ouattara
Mr Gbagbo has tried to clamp down on protests by ordering an overnight curfew throughout the country.
The UN says about 500 people, mainly pro-Ouattara supporters, have been killed since the election results were announced at the beginning of December.
Amnesty said it had documented serious human rights abuses in Abidjan and in the west of the country where an estimated 70,000 people have been forced to flee their homes.
One victim from the western town of Duekoue described how she had been set upon by gangs wielding knives and machetes last month.
"They broke the door and grabbed me. Their faces were blackened with charcoal," she said.
"They raped me, three or four of them. They burned my house - the house of my family - and they killed my brother.
"They stole everything from my shop and then burned it down. We fled the same day."
Investigators say scores of people have disappeared with reports that some are being held at the headquarters of elite government security forces.
"The eyes of the world may have shifted from the political stalemate... but the abuses are clearly continuing," Gaetan Mootoo, one of the Amnesty researchers, said in a statement.
"The current crisis has created a human rights black hole in the country."
November's presidential vote was supposed to reunify the West African nation, which has been divided between north and south since a conflict in 2002.