Guillaume Soro said days of clashes in Abidjan created panic among troops loyal to Gbagbo, who has refused to leave office since a November runoff despite the international community's recognition of Ouattara as the winner, the BBC reported Monday.
A spokesman for the U.N. mission in Ivory Coast said fighting was heard near the presidential palace where Gbagbo was believed to be staying.
An official within the Ouattara camp said there was a lull in the fighting as reinforcements arrived from the country's north.
Soro said Sunday pro-Ouattara forces had surrounded Abidjan.
"The situation is now ripe for a rapid offensive," Soro said on TCI, a Ouattara television station. "The operation will be rapid because we have discovered the exact number of operational tanks on the ground. Ivorians must trust in the Republican forces."
Abdon George Bayeto, a spokesman for Gbagbo, told the BBC Monday the incumbent was prepared to fight and accused the international community of plotting against him.
"When it comes to a fight we are going to put up a fight," he said. "The president is not going to step down."
On Sunday, U.N. Secretary-General Ban Ki-moon pressed Ouattara to investigate a massacre in Duekoue. Ouattara denied his forces were responsible but said he ordered an investigation and would welcome an international inquiry, U.N. spokesman Martin Nesirky said.
A U.N. human rights official blamed 220 deaths on Ouattara's forces and 100 on the retreating pro-Gbagbo army. Some reports had a death toll as high as 1,000.