The two journalists - the newspaper's defence correspondent Rupert Hamer and photographer Philip Coburn - were accompanying a patrol to the north west of Nawa when the vehicle in which they were travelling struck an improvised explosive device.
Despite the best efforts of medics at the scene Mr Hamer died of his wounds. Mr Coburn remains in a serious but stable condition.
One US Marine was also killed in the explosion. Five US Marines were left seriously injured.
Defence Secretary Bob Ainsworth said:
"Both Rupert Hamer and Phil Coburn accompanied me on my most recent trip to Afghanistan. I got to know them well and I was impressed by their hard work and professionalism.
"My thoughts and deepest sympathies are with the families, friends and colleagues of both men at this extremely distressing time.
"As a defence correspondent, Rupert Hamer was in regular contact with press officers at the MOD. I know they had great respect for his work and the news of his death has been met with great sadness amongst us all.
"In recent weeks we worked closely with Rupert on a special Christmas edition of the Sunday Mirror, containing messages for deployed personnel from their loved ones.
"The paper was very well received by troops on the ground and its success is testament both to Rupert's hard work and his understanding of Service personnel.
"The sacrifice of Service personnel is well documented and rightly respected, but this news demonstrates the risks also faced by journalists who keep the public informed of events on the front line."