Security in Basra had been steadily declining well before the British handed over responsibility for security to the Iraqis on Dec. 16.
British troops remained at their base at the airport outside Basra and were not involved in the ground fighting Tuesday, according to the British Ministry of Defense. Air support was being provided, but a spokesman could not say if it was US or British planes.
"We have a capacity to provide air and other specialist support if needed, but at this time British involvement is minimal," the spokesman said, declining to be identified in accordance with department policy.
Last month, a British journalist working for CBS and his Iraqi interpreter were kidnapped from a hotel. The Iraqi was released after al-Sadr's office negotiated a deal, but the Briton remains in custody.
"We are calling for calm, but this new security plan has the wrong timing," Harith al-Edhari, the director of al-Sadr's office in Basra, said Tuesday. "This plan is a government scheme to target the Sadrists as they did in Diwaniyah and Muthanna."
Al-Sadr's followers have accused the Shiite-dominated government of targeting their followers in advance of provincial elections expected this fall. They have demanded the release of supporters rounded up in recent weeks.
The cleric recently told his followers that although the truce remains in effect, they were free to defend themselves against attacks.
US officials have insisted they are not going after Sadrists who respect the cease-fire but are targeting renegade elements, known as special groups, that the American military believes have ties to Iran. Tehran denies allegations it is fueling the violence.
In other violence, two bombs exploded in central Baghdad, killing one civilian and wounding eight others, and a US-allied Sunni fighter also was killed in a drive-by shooting northeast of the capital, police said.