Foreign aid and reconstruction companies in Kabul tightened security yesterday after Taleban militants claimed responsibility for the killing of a Briton which shattered months of fragile calm in the Afghan capital. Westerners living in Kabul have been advised to keep a low profile and avoid moving around at night after the shooting of the British consultant to the Afghan government, diplomats said yesterday.Police say they are baffled why Steven MacQueen, an adviser to the Rural Development Ministry, was killed in an ambush on Monday night by gunmen driving four-wheel-drive vehicles. "It is a little bit early to say how it's going to affect the international community because we don't know yet what are the reasons related to this incident," Jean Michel Emeryk, of the Afghanistan NGO Security Office (ANSO), told Reuters. "For the time being, we are advising people to limit their movement during hours of darkness."