Queen Elizabeth marks end of British war in Afghanistan
The prayers will be followed by a procession through London and a flypast on Friday
Britain paid tribute on Friday to its soldiers who died and served in Afghanistan with a memorial service at St Paul's Cathedral attended by Queen Elizabeth II.
Archbishop of Canterbury Justin Welby led the service, which drew a line under Britain's 13-year involvement in a conflict that cost 453 British lives.
"Today is a moment for us to say thank you," Welby told the thousands-strong congregation, blessing a cross made of shell casings that adorned a wall at Britain's Camp Bastion base in southern Afghanistan.
Prince William, his wife Kate and brother Prince Harry also took part in the service. Former prime minister Tony Blair, who decided to deploy troops in the wake of the September 11, 2001 attacks, also attended.
The prayers will be followed by a procession through London and a flypast on Friday in contrast with a rapid and low-key withdrawal in October when the last combat troops were airlifted out of Camp Bastion.
Afghan President Ashraf Ghani told the BBC in an interview that Britain's fallen had "paid the ultimate sacrifice to enable us to live in freedom, in hope for peace, prosperity and dignity".
A total of around 150,000 UK personnel were deployed to Afghanistan during the conflict.
Blair told the BBC that in 2001 he "couldn't foresee how long these campaigns are going to be".
"I always felt that it was right and justified that we were there in Afghanistan, fighting both to remove the Taliban and then to stabilise the country," he said.
He also spoke of the current conflict with the Islamic State group, saying it was "a generational struggle".