David Cameron said Britain has "paid a heavy price" for its involvement in the conflict in Afghanistan as he visited troops there in the run-up to Christmas.
However, the Prime Minister said the campaign had been a success and that Britain and other Coalition forces had stopped the country becoming a "haven for terror".
He dismissed fears Afghanistan would see a "Taliban resurgence" when coalition troops leave and defended plans for British forces to be almost halved to 5,200 next year.
Full withdrawal is due to be completed by 2014.
Mr Cameron said that the Afghan security forces were doing "better than expected".
He insisted the withdrawal was being "done for good military reasons and it has been done in a proper way".
He said: "We're confident it can be done while making sure Afghanistan does not return to become a haven of terrorism which is of course why we came here in the first place.
"We have paid a very heavy price but I think the reason for coming here in the first place, which was to stop Afghanistan being a haven for terror ... I think it was the right decision," he added.
Mr Cameron toured Camp Bastion in Helmand, and saw vehicles which are being sent home because they are no longer needed after troop numbers in the country were cut by 500 to 9,000 this Christmas.
He moved on to Camp Price, a smaller base, 20 miles from Bastion, where he joined in a carol service with troops from 40 Commando Royal Marines, singing Once In Royal David's City and God Rest Ye Merry Gentlemen.
Mr Cameron lost 2-1 when he took on a marine at table football, saying afterwards: "Someone better take over the blue team."
The Government has pledged an extra £230m for military equipment, much of which will be extra kit to detect and counter roadside bombs.
The money from the Treasury reserve is being made available immediately. Officials said it demonstrates the determination to see the Afghanistan campaign through.