Foreign Secretary William Hague urged the Afghan people not to allow a "terrible" attack on a Kabul hotel to derail efforts to boost the country's security.
At least 10 civilians - mostly hotel workers - were killed during a four-hour assault on the Inter-Continental Hotel by heavily armed Taliban fighters.
Gunmen on the roof were killed by Nato helicopters as domestic security forces dealt with suicide bombers and other militants on the ground.
The assault began last night on the eve of a two-day conference about the transfer of security control to the Afghans by the end of 2014.
Mr Hague said: "The United Kingdom condemns the attack on the Inter-Continental Hotel in Kabul in the strongest terms.
"Our thoughts are with the families and friends of the victims of this terrible crime. Acts of terrorism such as this not only show contempt for human life but also seek to undermine public confidence in the progress that has been made in Afghanistan.
"We should not, and the Afghan people should not, let incidents such as these shake our joint resolve to build a safer and more secure Afghanistan."