The Taleban commander responsible for increasingly sophisticated bomb attacks on British soldiers in Afghanistan is a former detainee of Guantánamo Bay released from prison in Kabul last year by Hamid Karzai’s Government, The Times has learnt.

Abdullah Ghulam Rasoul was held in Guantánamo for six years before being released to Afghan authorities in December 2007, after a US military review board decided unanimously that he was no longer a threat.

British and Taleban officials have told The Times that Rasoul has since resurfaced as Mullah Abdullah Zakir, the Taleban’s new operations chief in Helmand and the architect of a new offensive against British troops.

Since he took over, the “asymmetric” threat from the Taleban has risen dramatically, with greater numbers of more sophisticated and powerful roadside bombs used against British troops. “He is a serious player,” one Whitehall official said.

Although Rasoul was released from Guantánamo after convincing interrogators that he had never held military command, Taleban officials told The Times that he had been a high-ranking commander close to the Taleban’s supreme leader, Mullah Omar.

The disclosure will complicate further President Obama’s efforts to persuade countries to take in Guantánamo detainees and allow him to close the camp within a year as promised.

Rasoul was captured in the chaos of the Taleban surrender at Kunduz, northern Afghanistan, in December 2001. He was in the lead car of a convoy of senior Taleban leaders, carrying a Kalashnikov and two Casio watches later identified as key components of home-made bombs. Rasoul denied that the watches were his, but it now appears likely that they were evidence of his expertise in bombmaking.

British officials believe that he is the mastermind behind the deadly surge in roadside bombings in Helmand since spring 2008, when he was released from Pul-e-Charkhi prison, Kabul.

Forty-four British troops have been killed in roadside bombings since 2008 and 18 in direct exchanges of fire. In 2007 15 Service personnel were killed by bombs and 15 in direct fire.British officials and Taleban sources said that Rasoul was believed to be based in Quetta, Pakistan. “He is back in Helmand since his release,” a Taleban commander told The Times. “He is in the border area now, sometimes in Pakistan and sometimes in Afghanistan. He is a very big commander.”

Rasoul, known as Detainee 008 in Guantánamo, is the latest in a line of former inmates and released Taleban prisoners to return to the fight in Afghanistan, including Maulavi Ghulam Dastagir, who was released on the personal orders of President Karzai.

Rasoul was one of 13 Afghan prisoners flown home to Kabul on December 12, 2007. On his return, he was placed in Block D of the Pul-e-Charkhi maximum security prison, renovated by the Americans for the detention of prisoners transferred from jails at Bagram and Guantánamo.

He was released early in 2008, soon after President Karzai appointed a high-level commission to rule on the detainees’ fate. The circumstances of his release remain unclear.

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