Christmas celebrations are cancelled in Basra this year to mourn the killing of a Christian brother and sister.

The pair were shot dead by militiamen barely a week before British troops hand control of security in the province to the Iraqis, convinced that their job is done.

The Most Rev Imad al-Banna, the Archbishop of Basra, said that he had asked the city’s significantly reduced Christian community not to put up Christmas trees or give presents. Religious ceremonies over the festive period, however, will continue as planned. “It is just to show how sad we are to lose our people and also to reject the killing of any innocents,” Bishop Banna told The Times.

“We have asked people not to put up trees and not to exchange Christmas gifts. We also ask God to forgive the people who killed the two martyrs and to guide them to the right path.”

The instructions came after the bullet-riddled bodies of Osama and Maison Marzouq were found in a rubbish dump on Monday. Gunmen in a vehicle had seized Osama, 31, the previous day and told him to telephone his 41-year-old sister to ask her to meet him, police said.

The Archbishop said that the motive for the killings was still unknown, but tried to play down fears of sectarian divisions in Basra, noting that Christian and Muslim mourners attended the funeral service for the brother and sister. “Just as we have Christians getting killed in Basra, innocent Muslims are also killed every day,” Bishop Banna said, adding: “Because we [Christians] are in the minority, a single incident will become more significant and evident.”

The double murder, however, left other Basra-based Christians terrified; several refused to be interviewed about the situation for fear of becoming targets. Fadi, a Christian school teacher, agreed to talk but declined to give his full name.

“Just as we started to see some improvement in the security situation this incident of Osama and his sister happened, bringing fear back into the city and particularly to a Christian family especially at Christmas time,” he said.

Intimidation by extremist gangs and other violence has forced thousands of Christians to flee Basra since the 2003 invasion. The city’s Christian population now stands at about 3,000, down from 20,000 before the war.

The Archbishop’s advice comes as British forces prepare to hand control of security in Basra to the Iraqi authorities on Sunday. It will be the last of the four provinces secured by Britain in southern Iraq since the war to return fully to Iraqi hands.

British commanders admit that security in the oil-rich port city – plagued by Shia militias, some backed by Iran – is not ideal. They feel, however, that the Iraqi Army and police are sufficiently well trained to take charge. This will enable Britain to cut its troop presence from 4,500 to 2,500 by next spring as it adopts an ever greater backseat role.

A British military spokesman in Basra described the deaths as a “tragic incident”. Major Mike Shearer said: “There are clearly still malign influences that try to unsettle the relative calm in Basra. The Iraqi security forces and the larger community in Basra are meeting this challenge head on with our support.”

The Christian schoolteacher was less convinced, despite holding out some hope that the improved competence of the Iraqi forces would produce results. “We as Basra locals and particularly Christian families are still worried about the future of this city. We see an uncertain future ahead, that’s why we are worried and afraid,” he said.

A British soldier involved in a road accident in southern Iraq on Wednesday has died from his injuries. The soldier was a member of 1st Battalion The Scots Guards. His next of kin have been informed.

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