Some 2,000 youths are burning tyres and throwing stones outside a UN base in the main city, Abidjan, while UN troops have responded with tear gas.
Protests by Gbagbo supporters erupted on Monday after UN-backed mediators recommended dissolving parliament, whose mandate has expired.
Ivory Coast, the world's largest cocoa producer, hosts about 7,500 UN troops.
In New York, the UN Security Council has issued a statement condemning the unrest and threatening sanctions against individuals blocking the peace process.
Ivory Coast has been split in two since a failed coup in 2002.
A UN spokesman said the protesters had set fire to a car and were trying to provoke the peacekeepers.
HAVE YOUR SAY
There are also protests outside other UN bases in the loyalist south, he said.
The BBC's James Copnall in Abidjan says the pro-Gbagbo group, the "Young Patriots", are in control of virtually all the main streets in the city.
Roadblocks have been set up and many people cannot get to work.
He says the city seems slightly busier than on previous days and some shops have reopened, but there are hardly any privately owned buses or taxis running.
'Remove Gbagbo'
On Wednesday, Mr Gbagbo called for his supporters to end attacks on UN peacekeepers and urged the people of Abidjan to return to work.
But some protesters have refused, saying the UN should be punished for a clash earlier in the week that left at least four people dead.
IVORY COAST CONFLICT
Mr Gbagbo assured supporters that only the president and prime minister could decide whether to dissolve parliament, a fact he said had got lost in the fury of the past few days.
He issued the statement after meeting Nigerian President Olusegun Obasanjo, in an effort to restore calm.
But a senior Nigerian politician claimed Mr Gbagbo was part of the problem, not the solution.
"We have to remove him from the scene... and use the absence to secure the peace and to move gradually towards properly elected government," Usman Bugaje, the chairman of the Nigerian House of Representatives' foreign affairs committee, told the BBC.
On Wednesday, some 2,000 Ivorians loyal to Mr Gbagbo surrounded the UN headquarters in Abidjan, and were held back by tear gas and rifle fire.
And more than 300 troops were forced to withdraw from two UN bases in the west of the country after clashes killed at least four protesters.
One Abidjan businessman told the BBC News website how a 150-strong mob had broken into the underground car park of his apartment block, where several UN civilian staff also live, on Monday.
"They wrenched the car park gate off its hinges and trashed two vehicles with UN markings on them," said the man, who preferred to remain anonymous for security reasons.
International concern
Following the mediators' call for parliament to be dissolved, the ruling Ivorian Popular Front (FPI) pulled out of the transitional government and UN-backed peace talks, and called on the French and UN troops keeping the peace to leave.
Elections were due to be held last year but were postponed because of the continued instability.
Analysts say by calling for the dissolution of parliament, mediators intended to strengthen Prime Minister Charles Konan Banny's authority and ensure that hostile deputies did not block attempts to implement the peace process, as happened last year.
But Mr Gbagbo's FPI party accused the international community of carrying out a "constitutional coup d'etat".
A spokesman for the rebel New Forces, which hold the north, responded: "There is not a future for Ivory Coast if the FPI succeeds in making a putsch against the peace process. That means war."
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