Kabul, Afghanistan — The first British woman killed in action in Afghanistan has died along with three SAS reservists in the deadliest enemy attack on British forces since hostilities began nearly seven years ago.

In one of the bloodiest periods of the conflict, nine British soldiers have died in the past 10 days, bringing the total number of deaths to 106 since the start of military operations in November 2001.

It came just days after the government announced that around 200 more troops are being sent to the country, taking the British force to a new high of 8,030 by next spring.

The sharp upturn in violence against British troops in recent weeks followed a period of relative stability and has raised fears of a Taliban summer offensive. The Taliban are increasingly using suicide bombers and sophisticated weaponry — possibly supplied by Iran — instead of fighting openly.

The death of four soldiers was the single biggest loss of life to hostile action in Afghanistan. Enemy action was not a factor in the biggest single loss of life, when an RAF Nimrod crashed in September 2006, killing 14.

The soldiers’ Snatch Land Rover was hit by an explosion near the capital of Helmand province, Lashkar Gah, on Tuesday afternoon.

The vehicles have been repeatedly criticized for not providing enough protection against roadside bombs.

Experts have called for them to be fitted with electronic countermeasures, and for the deployment of more helicopters.

A Conservative member of Parliament and former Army officer, Patrick Mercer, said: “Helicopters are still vulnerable, but they’re not vulnerable to this sort of weapon.”

The female soldier who died was a member of the Intelligence Corps, which does one of the most delicate jobs in Afghanistan, collecting information and winning over local contacts to counter-insurgency efforts.

She was the first British woman soldier to die in Afghanistan, but five have died during operations in Iraq since the 2003 invasion.

The three men were from 23rd Special Air Service Regiment, one of two Territorial Army SAS units.

All four are expected to be named today after the Ministry of Defence changed its policy about keeping the names of special forces fatalities secret.

They were involved in an operation to train Afghan security forces.

A military source said: “It was part of the training they are giving the Afghans. There was a large explosion, they were in a convoy but they were the one vehicle that was pretty badly hit.”

Military explosives experts will visit the scene to establish the exact nature of the bomb, but it was believed to be an improvised explosive device or a mine.

A fifth soldier was wounded and was in a stable condition after being evacuated to the British desert military base at Camp Bastion in Helmand.

Last week, more than 1,000 prisoners, including hundreds of Taliban, broke out of the main prison in Kandahar, southern Afghanistan’s biggest city, in the province neighboring Helmand.

NATO and Afghan forces began a three-day offensive after many of those from the jail took over villages on the outskirts of the city. At least 20 insurgents were reportedly killed.

Prime Minister Brown said the British mission in Afghanistan was the “noblest of causes” and denied soldiers were being failed by poor equipment.

He told MPs that the Taliban had changed tactics and new equipment would be provided to cope with that.

Mr. Brown said: “They are no longer fighting as an army, they are fighting as an insurgency. That’s why we are seeing mines and roadside bombs, that is why we are reordering the way our forces work and that is why we are taking new equipment to Afghanistan.”