Four people have been shot dead in Ivory Coast's main city, Abidjan, after a march to protest about the killing of seven female demonstrators last week.
Journalists have seen the bodies of three men and a woman in clinic.
The shooting has been blamed on rogue army officers supporting disputed President Laurent Gbagbo.
He refuses to cede power although his rival Alassane Ouattara is internationally recognised as the winner of last year's poll.
News of the latest trouble came as the US said Mr Gbagbo's order for the government to take control of all cocoa purchases and exports "amounts to theft".
"It is another desperate act in his campaign to cling to power," US state department spokesman PJ Crowley told journalists.
Ivory Coast is the world's biggest cocoa producer - the cocoa sector accounts for 40% of global supplies and is currently dominated by multinational companies.
Last month, Mr Ouattara called for a temporary ban on exports to try to force Mr Gbagbo from power.
The UN-backed electoral commission says Mr Ouattara won presidential elections in November, but the Constitutional Council overruled it, citing rigging in the north.
The protest march in Abidjan's central Treichville district had passed off peacefully before shots were heard, journalists say.
Hundreds of demonstrators had planned to march to mark International Women's Day.
"They were hit by bullets," said a medical official who declined to be named, reports the AFP news agency.
"Two arrived dead and two died at the clinic from their wounds."
The AP news agency says the clinic was overwhelmed.
Some 300,000 people have fled their homes in Abidjan following fighting in the city in recent weeks, according to the UN refugee agency.
Another 70,000 have fled violence in the west, seeking sanctuary across the border in Liberia.
Meanwhile, Mr Gbagbo has declined an invitation to attend an African Union meeting in Ethiopia on Thursday.
He had been invited along with Mr Ouattara to hear the AU's intended resolution to the crisis; instead he is sending the head of his party and his foreign minister - two known hardliners.
The BBC's John James in Abidjan says if the AU mission fails, it is likely to increase the chances of a return to civil war.
He says things remain calm along most of the former ceasefire line between the pro-Ouattara New Force former rebels in the north and the pro-Gbagbo army in the south.
But in the far west, where the former rebels have been taking territory, movement seems aimed at securing areas around the town of Toulepleu, which was captured on Sunday.
Publicly the New Forces says their objective is to cut off access to Liberian mercenaries rather than to move on to bigger towns in the south and east.
Our reporter says cocoa goes right to the heart of the conflict between Mr Gbagbo and his rival Mr Ouattara.
The price of cocoa has been trading at its highest levels for a year, as supplies have been strangled by recent sanctions and the near collapse of the banking system.
The European Union, US and West African states have adopted various financial sanctions against Mr Gbagbo and his closest allies.
Exporters have stopped registering new beans for export - as a result, there is close 500,000 tonnes of cocoa piling up in port warehouses. Up country, the market has collapsed for the estimated 700,000 small holder cocoa farmers.
Given the financial crisis since the election, it is very difficult to see how the government will be able to implement its radical reforms of the cocoa sector, our reporter says.