Three British soldiers died after their armoured vehicle was hit by a roadside bomb in Afghanistan on Tuesday.
Six other soldiers were wounded in the blast in Helmand province on a routine patrol in the district of Nahr-e Saraj.
The BBC reports the number of British service personnel to have died since operations in Afghanistan began in 2001 is now 444.
"We have paid a very high price for the work we're doing in Afghanistan," Prime Minister David Cameron told ITV television.
"It is important work because it's vital that country doesn't again become a haven for terrorists - terrorists that can threaten us here in the UK.''
The three soldiers from the Royal Highland Fusiliers infantry battalion died when their vehicle was hit on a routine patrol in the district of Nahr-e Saraj.