Baitullah Mehsud, the leader of the Pakistani Taleban, threatened yesterday to launch an attack on Washington that would “amaze everyone in the world” as he claimed responsibility for the raid on a police academy in Lahore and boasted of a new regional militant alliance.

Mr Mehsud, for whom the United States offered a $5 million reward last week, said that Monday's raid, which killed seven police officers, was retaliation for US drone attacks on Pakistan's northern tribal areas, now the main hub of Taleban and al-Qaeda activity.

The 35-year-old leader of Tehrik-e-Taleban Pakistan (Movement of Taleban Pakistan), made the claims after taking the highly unusual step of telephoning Western news organisations from an undisclosed location.

“We wholeheartedly take responsibility for this attack and will carry out more such attacks in future,” he said.

“Soon we will launch an attack in Washington that will amaze everyone in the world ... The maximum they can do is martyr me. But we will exact our revenge on them from inside America.”

Mr Mehsud's threat illustrates his growing confidence in the Pakistani Taleban's strength and reach. He recently agreed to shelve differences with fellow commanders and join forces with the Afghan Taleban.

The alliance appears to be a deliberate response to President Obama's “Afpak” strategy, unveiled on Friday, to send 21,000 more troops to Afghanistan, pour $7.5 billion into Pakistan, and to treat the two countries as a single military theatre.

Mr Mehsud's power also appears to have been enhanced after the Pakistani Government reached a controversial peace deal with the Taleban in the northwestern Swat Valley, which borders the tribal areas. He has been blamed for several attacks in Pakistan, including the assassination of Benazir Bhutto in December 2007, but most have been in the north west, and Monday's was thought to be his first on the eastern province of Punjab.

The US Rewards for Justice website describes him as a “key al-Qaeda facilitator” who has conducted cross-border attacks against American forces in Afghanistan and poses a clear threat to American people and interests in the region.

The militant leader boasted that he had recently set up a “Council of Mujahidin” uniting different groups “to step up attacks on US and Nato forces in Afghanistan”. That tallies with other reports that the Afghan and Pakistani Taleban have joined forces, and are also working with outlawed Pakistani militant groups with links to Pakistan's Inter-Services Intelligence (ISI) agency.

The Pakistani Taleban is led by Mr Mehsud and two rival commanders - Hafiz Gul Bahadur and Maulavi Nazir - who are all based in the tribal regions of North and South Waziristan and have long feuded with each other.

Mullah Omar, the Afghan Taleban leader, is reported to have sent a six-member team to Waziristan in late December and early January to forge a new alliance with the three men against the planned increase of American forces in Afghanistan.

The Pakistani Taleban leaders agreed, and in February they formed the Council of Mujahidin and issued a printed statement vowing to resolve their differences and focus on fighting US-led forces in Afghanistan.

However, they also appear to have enlisted elements of Pakistani militant groups such as Lashkar-e-Taiba (LeT), blamed for the attack on Mumbai last year, and Lashkar-e-Jhangvi, blamed for last month's attack on the Sri Lanka cricket team in Lahore.

They, along with elements of Jaish-e-Mohammed (JeM), another banned militant group, give the alliance a presence in Punjab, which may explain the two recent attacks there, security officials and analysts say.

“Many former fighters of LeT and JeM, and from southern Punjab, have been fighting with the Pakistani Taleban,” one Pakistani security official told The Times.

Most experts agree that the militant alliance is fragile, especially since Mullah Omar wants to focus on Afghanistan, while Mr Mehsud and others have ambitions in Pakistan, but it still represents a major challenge to Mr Obama's new strategy.

Michael Semple, an Irish expert on the region who was the former deputy head of the European Union mission in Kabul, predicts that some militants can be split from the group's core if governance and security are improved.

“It can be done, and we do have a few demonstrated examples that prove that it is possible,” he said. “But a lot of things are going to have to be done right if it is going to deliver enough people to be able to make a difference to the conflict.”

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