LONDON, England (CNN) -- British troops began their formal withdrawal from southern Iraq Tuesday, "marking the beginning of the end of the UK's six-year combat mission in Iraq," the Ministry of Defence announced.

The remaining 4,000 or so British troops in the sector will leave by summer, a ministry spokesman told CNN.

The spokesman declined to be named in line with MoD policy.

"You won't now see hundreds of troops coming out of Iraq every day, (but) this is the start of the end for British forces -- a period that will take until the end of July," the spokesman said.

The British headquarters staff of about 40 people is pulling out of Basra Tuesday, lowering the flag of their command, Multi-National Division Southeast in Basra, as military control of the region passes to the United States.

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