Former rebels in Ivory Coast have warned that a row over a controversial nationality law could rekindle the country's civil war.
President Gbagbo has been accused of sabotaging peace efforts
New Forces spokesman Sidiki Konate dismissed the African Union's idea that a referendum on the issue might be a way forward for the peace process.
MPs last month voted to scrap a ban on candidates of not purely Ivorian parentage standing for president.
President Laurent Gbagbo then called for a referendum on the issue.
South African President Thabo Mbeki met Mr Gbagbo on Tuesday in a further effort to end the civil war.
Mr Mbeki's visit to Ivory Coast follows a summit of African Union (AU) leaders in Gabon on Monday which called on the United Nations to reinforce its peacekeeping presence in Ivory Coast and beef up its mandate.
According to the BBC's James Copnall in Abidjan, President Mbeki met as many people as possible during his short stay.
But Mr Konate said the opposition New Forces - which control the north of the country - would only meet Mr Mbeki in South Africa for security reasons.
Mr Konate told the BBC's Focus on Africa programme that the proposed referendum would be a "big mistake".
The AU security summit said that such a referendum was one option for easing tension.
The nationality law, in the form of a constitutional amendment, has been a key sticking-point in the peace process and its scrapping would allow the main opposition candidate Alassane Ouattara to stand.
In an interview with French TV, the exiled president of the Rally of Republicans, said a referendum would be a step in the wrong direction.
"I cannot see how you can hold a referendum soon in a country which is split in two, where there is no electoral register and where the majority of citizens have no identity cards to vote," he said.
Our correspondent says President Gbagbo's Ivorian Popular Front (FPI) is delighted with the AU's announcement.
FPI leader Pascal Affi Nguessan said that it showed that democracy was the way forward for the country, he says.
But opposition politicians fear that if such a referendum is held, and the amendment reversed, the opposition will be left at a disadvantage in future presidential elections.
There is also confusion amongst opposition parties over the exact meaning of the AU's statement, as a referendum was mentioned as one of a number of possibilities, our correspondent says.
At the summit, African leaders also called for an extension of the deadline on a second round of UN sanctions, which would include the freezing of assets of people who are not engaged in the peace process.
The AU wants the UN's mandate to be beefed up
This is intended to give Mr Mbeki more time to convince all sides in the conflict that disarmament and constitutional reforms can make presidential elections feasible within 10 months.
The AU's Peace and Security Council also addressed other African conflicts:
- On the conflict in Sudan's western region of Darfur, it called on African states pledging peacekeepers to ensure their commitments are honoured in time
- On the Democratic Republic of Congo, the AU resolved to help the country in disarming and neutralising militias linked to Rwanda's 1994 genocide.