Rockets have been fired at a plane carrying Ivory Coast Prime Minister Guillaume Soro, who was not hurt in the attack, his New Forces group says.
Mr Soro reached a deal with his former foe, President Gbagbo
At least three people were killed in the attack in Bouake, the headquarters of Mr Soro's former rebel group.
Reinforcements have reportedly been rushed to Bouake airport and shooting was reported in the town.
Mr Soro was named prime minister in April under a deal to end Ivory Coast's four-year division.
New Forces spokesman Cisse Sindou told the BBC's Focus on Africa programme that three rockets were fired from Bouake's airport as Mr Soro's plane was landing.
"There were some injured that are being treated now at the hospital. Mr Soro is in his office working - he had no injuries. He's very fine and very alive," Mr Sindou said.
The incident would not affect the peace process started in March, Mr Sindou said, adding that there had been a number of arrests.
"I think it's just three guys that did that. It was not an organised type of thing that did the attack," he said.
However the BBC's James Copnall in Ivory Coast says it is bound to affect the fragile peace - even just by discouraging civil servants from returning to the former rebel-held north.
He says most people will suspect New Forces members who are unhappy with the peace deal could be behind the attack.
Many former rebels are unhappy that Mr Soro accepted the job of prime minister serving under their sworn enemy, President Laurent Gbagbo, our correspondent says.
French Foreign Minister Bernard Kouchner condemned the "cowardly attack", urging all parties to stick to the timetable for peace.
New Forces rebels seized northern Ivory Coast in September 2002 and accused President Gbagbo of discriminating against northerners and Muslims.
Mr Gbagbo and Mr Soro agreed a deal to reunite the country and hold elections, which have repeatedly been cancelled.
Under that deal, a buffer zone patrolled by United Nations and French peacekeepers between the two forces has been dismantled.
There has been no serious fighting since November 2004, and in recent times the peace process had seemed to be making real progress, our correspondent says.