The army surrounded the TV station and clashed with supporters of Alassane Ouattara Soldiers loyal to Laurent Gbagbo, one of Ivory Coast’s would-be presidents, have fired on protesters trying to take control of state TV and killed at least three people, reports say.
Violence has spread throughout Abidjan, with witnesses reporting gun battles near the hotel of Alassane Ouattara, who also claims to be president.
Mr Ouattara’s spokesman said the hotel was under attack.
The army earlier accused protesters of inciting confrontation.
Mr Ouattara and Mr Gbagbo both claim to have won last month’s election, and each has declared himself president.
The UN, which backs Mr Ouattara’s claim, has urged calm.
The BBC’s John James in Abidjan says there is high security around the television station, with tanks blocking the main boulevards.
He says shops and offices are closed, with only protesters and security forces out on the streets.
Mr Ouattara’s supporters had planned to march on the offices of state TV, which has been broadcasting reports praising Mr Gbagbo since the disputed election.
But his supporters clashed with security forces in the north of Abidjan early on Thursday.
International news agencies reported at least three protesters were killed after police opened fire on the crowds.
AFP news agency also said at least one protester had been killed in another part of the city.
Separately, in the south of the city, gun battles erupted between soldiers who control the area and former rebels who are guarding the hotel where Mr Ouattara has been based since the election.
Mr Ouattara’s supporters, including his nominated prime minister Guillaume Soro, were trying to leave the hotel compound and march to the TV station when fighting broke out.
A spokesman for Mr Ouattara told the BBC that they were coming under attack.
Earlier in the day, international prosecutors said they would bring legal proceedings against anyone accused of causing deaths.
And UN Secretary General Ban Ki-moon’s spokesman warned that “those who incite or perpetrate violence, and those who use the media for that purpose… will be held accountable for their actions”.
He reiterated that the UN wanted Mr Gbagbo to stand down.
The UN, which has about 10,000 peacekeepers in the country, is guarding Mr Ouattara’s hotel alongside fighters from Mr Soro’s former rebel group the New Forces (FN).
The FN still controls the north of the country, which was split into two after a civil war in 2002.
The trouble stems from last month’s run-off election, which the Electoral Commission said Mr Ouattara won by 54.1% to 45.9%.
Mr Gbagbo refused to admit defeat, and the Constitutional Council then annulled some results from the north and declared Mr Gbagbo the winner.
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