The withdrawal of 1,600 British troops from southern Iraq by the spring has been thrown into uncertainty amid claims of an increase in killings and intimidation by Shia militia in Basra.

Commanders have yet to make a decision on troop levels and time is running out to reduce the number of British troops in Iraq to 2,500.

Gordon Brown said in the autumn that a final decision on the hoped-for withdrawal would depend on conditions on the ground.

In a sign that the militia remain tough, a roadside bomb killed 14 mourners travelling in a bus to Basra from a funeral in Najaf yesterday. Eighteen people were wounded in the blast, which was aimed at a US convoygoing in the opposite direction.

Iraq timeline: five years of conflict

From accusations that the weapons of mass destruction dossier had been sexed-up to withdrawal of British troops from Basra

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Iraqi officials, who took control of security in Basra from the British in December, have asked Baghdad for up to 6,000 extra troops to help to quell the unrest, on top of a new brigade sent to the province last month.

Lieutenant-General Bill Rollo, the most senior British officer in Iraq, emphasised that the withdrawal plan hinged on assessments on the ground.

“There was a direction of travel and that is the aim and then we will judge it on conditions at the time, and that process is ongoing,” General Rollo said. “I am not going to try and anticipate what the final figure will be.”

Asked whether there was a potential for troops to stay longer, given that it was spring already, he said: “There is a process that we will go through and we will get to the figure and we will know what the aim is.”

As for when that would be, he said: “It will still be the spring in April.”

Four hundred soldiers left Iraq in January, taking Britain’s troop strength to about 4,100, mainly based at Basra airport, outside the city. With the Iraqi police and army in charge of security, British forces are largely involved in protecting their base as well as offering surveillance, intelligence and training to the Iraqis.

Many local people, however, feel that Britain relinquished responsibility for the oil-rich port too quickly.

“The British helped these militias to grow,” said Abu al-Razzaq al-Saedi, a lawyer. “Now they stay in the airport and leave us with the militia groups killing us and controlling the city.”

Several thousand people protested at the weekend over what they said was an increase in violence since the British pulled back. A neurologist, one of 12 left in Basra, was buried on Monday after being kidnapped and strangled, his arms and legs broken.

Determined to rein in the militant gangs, Iraqi commanders have been building up the Army’s 14th division in Basra. A third brigade of 3,000 soldiers was deployed to the province in February, with a fourth brigade due to follow in December. In addition a fourth brigade for the 10th division, which is also based in Basra, is due to arrive in September.

Basra was seen as an urgent case because of its strategic importance and also the potential for conflict, with rival Shia political parties and militias vying for control.

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