A "small minority" of Shias are to blame for the violence which hit Iraq during the weekend leaving scores dead, Tony Blair's spokesman has said.
Shia's have taken over the governor's headquarters
But Downing Street insisted that the unrest would not derail plans for a handover of power at the end of June.
The UK prime minister is to meet the Iraqi foreign minister on Tuesday.
Mr Blair's spokesman said: "The important thing to recognise is these actions are being carried out by a small minority of the Shia community."
Supporters of radical cleric Moqtada Sadr have been involved in violent protests in at least four Iraqi cities which have claimed the lives of at least nine coalition soldiers and 50 Iraqis.
The demonstrations were triggered by the closure of Mr Sadr's main newspaper a week ago; they intensified after the arrest on Saturday of one of his top aides, Mustafa Yacoubi.
Mr Sadr's supporters have taken over the governor's building in Basra, southern Iraq.
Mr Blair's spokesman said the situation was being taken seriously but Basra was now calm with UK troops working "in support of the governor and Iraqi police as they respond to the situation".
But he told reporters: "There is no change in our determination to meet the deadline
of June 30."
However, shadow foreign secretary Michael Ancram warned that issuing a specific timeline could be used by opponents of the transfer of power to create instability.
He urged the government to wait until nearer 30 June before deciding whether it was an achievable goal.
In Baghdad on Sunday, eight American soldiers were killed in gunfights.
Reporting from the roof of the building, BBC correspondent Dumeetha Luthra said dozens of militants belonging to Mr Sadr's Mehdi Army moved into the governor's office at dawn on Monday.
She said they were chanting "No to America, we'll sacrifice ourselves to Sadr" and waving pictures of their leader.
Hundreds more protesters gathered outside the building.
A Ministry of Defence spokeswoman confirmed that the occupation had been peaceful and said talks were under way between the protesters and Iraqi officials.
On Monday, the US administrator in Iraq, Paul Bremer, outlawed the Mehdi Army saying the coalition would not tolerate an uprising.
Many of Iraq's majority Shia Muslims - repressed under Saddam Hussein - welcomed last year's US-led invasion, and attacks on coalition forces were largely confined to the minority Sunni community before Sunday's violence.
However, Mr Sadr has become an increasingly outspoken opponent of the occupation.