About 20,000 people turned out for Friday's march
Georgia's opposition has begun a campaign of daily disruption in the capital Tbilisi in a bid to oust President Mikhail Saakashvili.
Activists blocked off major roads in the city for six hours and said they would repeat the closures between the same times each day.
They accuse Mr Saakashvili of leading the country into a disastrous war with Russia and provoking a crisis.
The president insists he will serve out his full term in office, until 2013.
He was speaking as the opposition held a new rally but the number of protesters - about 20,000 - was sharply down on the 60,000 reported on Thursday.
Some pelted the presidential residence with carrots and cabbages which they explained was "rabbit food" for a "cowardly" president.
The opposition announced a "national disobedience campaign" with roads to be blocked between 1500 and 2100 daily (1100-1700 GMT).
Correspondents say traffic in central Tbilisi was paralysed on Friday afternoon by marching demonstrators.
'Ultimatums every month'
As night fell on Friday, hundreds of protesters remained outside parliament.
Mr Saakashvili's critics say his style of government is autocratic
"We will stand here until the opposition's demands are met and we support these demands", Nino, an opposition supporter, told Reuters news agency.
"The president must resign, there can be no dialogue with him," said another protester, Guka Kvantaliani, speaking to AFP.
"He must resign because he lost our territory, he is not interested in the people and there is no justice in Georgia."
Rejecting the calls to quit, Mr Saakashvili said he was ready for a dialogue with the opposition "on strengthening [Georgia's] democratic institutions".
"I've been listening to ultimatums every month for the last five years... My term expires in 2013," he told reporters.
Opposition leaders have appealed to the government not to use violence to break up mass protests.
Police used rubber bullets and tear gas to break up the last mass protests in Tbilisi in November 2007.
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