(CNN) -- The British Defence Ministry Thursday identified six British soldiers who are missing and presumed dead following an explosion in southwest Afghanistan.
The Taliban claimed responsibility for the blast.
The soldiers were traveling in a tracked armored vehicle in Helmand province Tuesday when the explosion occurred, a British military official said.
The vehicle hit a land mine, setting off a substantial explosion, said the official, who spoke on condition of anonymity because of the sensitivity of the issue.
The area where the blast occurred was not on a paved road. It is in the Nar-e-Saraj area of Helmand, where Britain has lost many troops previously.
The ministry identified the soldiers as Sgt. Nigel Coupe, 33; Corp. Jake Hartley, 20; Pvt. Anthony Frampton, 20; Pvt. Christopher Kershaw, 19; Pvt. Daniel Wade, 20; and Pvt. Daniel Wilford, 21.
All of the soldiers, with the exception of Coupe, were assigned to 3rd Battalion, the Yorkshire Regiment, the ministry said. Coupe was assigned to 1st Battalion, The Duke of Lancaster's Regiment, it said.
If confirmed, the deaths in Tuesday's attack would be the most British troops killed in a single day in Afghanistan since six were killed on July 10, 2009, according to a CNN tally.
It was not immediately clear whether the explosion was caused by a roadside bomb.
There is a possibility the blast was caused by a "legacy device," a mine left over from the Soviet era, the military official said. Such devices have been found in that area, but there is no evidence leading to that conclusion at this point, he added.
It is also possible, even if it was an old mine, that it had been replanted by insurgents, he said.
On a Taliban website, the group claimed responsibility and described the explosive as a landmine.
Members of the NATO-led International Security Assistance Force reached the area, but will not officially confirm the deaths until they get into the damaged vehicle.
In a regularly scheduled conference call with U.S. President Barack Obama later Thursday, Afghan President Hamid Karzai said the security situation in his country had calmed "since events of recent weeks," White House Press Secretary Jay Carney told reporters.
Furor over the burning of Qurans at a NATO base in Afghanistan last month has fueled a string of protests and attacks that have left dozens dead, including four American soldiers. Hundreds more have been wounded in the attacks.
Carney said Thursday that the leaders also discussed continuing negotiations on a strategic partnership agreement.
CNN's Laura Perez Maestro, Tom Cohen and Nick Paton Walsh contributed to this report.