Taleban militants detonated a huge truck bomb south of the capital Kabul this morning killing 25 people, including 12 primary school children, according to local officials.

However, officials said they suspected the device was detonated prematurely after the truck crashed and had been intended for a "spectacular" attack on a target in Kabul ahead of presidential elections in August.

The blast in Mohammad Agha district of Logar Province, on the main route into Kabul from the south of the country, was powerful enough to throw pieces of the vehicle more than a mile, one local police official said.

“The blast has left 25 people dead,” Zmarai Bashiry, an Interior Ministry spokesman, told The Times.

“21 of the dead are civilians and four are policemen. Three nearby shops have been completely destroyed.”

Abdul Hamid, the district governor of Mohammad Agha, said that 12 of the dead were children attending a boy’s primary school close to the scene.

The police chief of Logar, Mustafa Khan, said that he believed that the truck was intended for a target in Kabul.

Officials said that the truck, which also contained a cargo of timber, appeared to have suffered a mishap and rolled into a stream at some point during the hours of darkness. When police arrived to clear the obstacle at 7am the insurgents detonated it remotely.

In recent weeks Western officials in Kabul have been receiving increased levels of intelligence "chatter" suggesting a Taleban plan to detonate a truck bomb in Kabul ahead of August presidential elections.

“There are certainly heightened threat warnings,” said one Western official.

“The election period presents security complexities and certainly everyone is a little bit tense about the possibility of an attack in the next eight weeks.” The most likely targets of the would-be "spectacular" attack were diplomatic missions, government buildings or the United Nations.

The last major Taleban attack in Kabul was in February when militants wearing suicide bomb vests carried out co-ordinated assaults on a number of government ministries, in an attack apparently intended to ape the Mumbai terror attacks. At least 20 people were killed but Afghan police commandos regained control within four hours.

Many Kabulis have noted tangible improvements to the police operating in and around the city in recent months, while the new Interior Minister, Hanif Atmar, has been widely praised for bringing greater coordination to Afghan security forces.

Some 4,000 additional police have been drafted into the city ahead of the elections, many of them from more thoroughly trained Civil Order police units.

With checkposts on all roads into the city, Kabul police have successfully thwarted a number of recent attempts to smuggle explosives into the city. Last week police recovered 150 kilograms of explosives from one vehicle but Taleban bomb cells are still thought to be still operating inside the city.

The bomb attack came as Nato announced the deaths of two further Western soldiers in the south of the country amid intense fighting in Helmand and across the south of the country.

British and US forces are involved in coordinated offensives against the Taleban in Helmand Province. The nationality of the two soldiers killed has not yet been announced.

Overnight 15 Taleban fighters were reported killed and another detained after a battle involving Afghan security forces and Coalition forces in the southern province of Zabul.

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