Defence Secretary Des Browne said on Thursday it would be some time before the number of British troops in Iraq was reduced.
Britain said last October it hoped to cut numbers from around 4,000 to 2,500 in the first few months of this year.
But at the start of this month, Browne confirmed that any reduction was being delayed amid recent unrest around Basra, southern Iraq, where most British troops are stationed.
In his latest update to parliament on the situation, he said it remained the plan to reduce force levels "as and when conditions allow."
"While the situation on the ground continues to evolve rapidly, and while military commanders continue to assess the changing environment in Basra, it remains prudent that we take time to fully consider further reductions," he said in a written statement.
"14th Division (the Iraqi army division in Basra) is still months away from becoming fully operational."
Browne announced that a new British brigade would take over providing the bulk of troops from June, and nearly 290 reservists would be called up as part of that to relieve existing personnel.
British forces handed Basra province over to Iraqi control in December last year and have since been involved in troop training and joint patrols.
Earlier this month, there were fierce clashes in Basra between Shiite militamen and Iraqi forces. British and US forces provided air support.
Former prime minister Tony Blair led Britain into the 2003 invasion as the key ally of the United States.
His successor Gordon Brown has sought to distance himself from association with the unpopular invasion since taking office last June.
He has appointed several critics of the conflict into his Cabinet and admitted that mistakes were made in the run-up to the invasion. (AFP)
Britain indicates no Iraq withdrawals for some time