The three UK troops killed in Afghanistan included two from the Household Cavalry Regiment and one from 7 Parachute Regiment Royal Horse Artillery, the Ministry of Defence said last night.
Three servicemen were killed when their patrol vehicle came under attack from insurgents in the Helmand province in southern Afghanistan, the bloodiest day for British forces since deployment in the region.
Just four hours earlier, a soldier serving with the 1st Battalion Light Infantry in Iraq became the first to die in an attack on a UK military base there.
The fatalities pushed the number of British service personnel who have died in Iraq since the start of hostilities in 2003 to 115, and saw the number of soldiers killed in Afghanistan in the past two months climb to nine.
Politicians responded to the deaths by calling on the Government to clarify its military strategy.
Labour MP Alan Simpson (Nottingham South), a long-term critic of the military campaigns, said the deaths were further evidence that Afghanistan had become "mission impossible", while Iraq was "mission irretrievable".
He said he believed that troops would have to be pulled out of both countries "soon" because there was "no longer a plan" to work to.
Liberal Democrat shadow defence secretary Nick Harvey said the deaths in Afghanistan underlined the need for a clear military strategy, with achievable objectives.
He said: "This is a vital mission, but with the head of Nato forces describing the country as `close to anarchy', the Government must be clear about the challenges ahead."
Responding to yesterday's heavy death toll, Defence Secretary Des Browne paid tribute to the efforts of British troops and stressed his commitment to operations in both countries.
He said: "Those responsible for the attacks on our soldiers in Northern Helmand do not want to see security and prosperity brought to the local people.
"We cannot allow them to succeed, and we remain committed to seeing through our part in this vital international effort.
"Nor will the sad death of a British soldier in Basra deflect our support to the elected government in Iraq."