The finding, based partly on unspecified communication intercepts, has dramatically heightened US concerns about long-standing ties between Pakistan’s Inter-Services Intelligence agency (ISI) and Taliban-allied groups that are battling US forces in Afghanistan, according to two US government officials briefed on the matter.

The July 8 bombing at the Kabul embassy has been linked to fighters loyal to Jalaluddin Haqqani, an ethnic Pashtun militant who has led pro-Taliban insurgents in Afghanistan and is linked to numerous suicide bombings in the region. The bombing killed more than 40 people in one of the deadliest attacks on civilians in Afghanistan in recent months.

“There continues to be evidence of Taliban and Haqqani network involvement in the Indian embassy bombing as well as the attempted assassination of (Afghanistan President Hamid) Karzai,” said a senior US official briefed on the reports. He said there was “significant” evidence suggesting that individual ISI members provided logistical support to the embassy bombers. He declined to elaborate further.

CIA officials raised the issue of possible ISI involvement during a meeting last month between the newly-elected Pakistani government and a delegation led by Steven Kappes, the agency’s director of clandestine operations. The visit was first reported by the New York Times.

The official stressed that the ISI has generally worked closely with US intelligence in battling al-Qaeda and Taliban forces in the rugged tribal region between Pakistan and Afghanistan.

“With Pakistan you have good cooperation in the counter-terrorism area and very legitimate concerns in others,” said a US counter-terrorism official knowledgeable about US ties with the ISI. “The Pakistani government, and the ISI in particular, are not monolithic. But the concerns we do have are well-founded and they have certainly not abated.”

Pakistani officials have repeatedly denied the allegation of ISI support for the Taliban.

Pakistani Prime Minister Yousaf Raza Gillani met with President George W Bush in Washington this week, with both leaders seeking to ease bilateral tensions over the conduct of the campaign against terrorism. Their talks focused on efforts to clamp down on al-Qaeda and Taliban extremists in Pakistan’s northwest tribal areas.

Gillani secured a pledge from Bush to respect Pakistani sovereignty in exchange for promises from Islamabad to crack down on the militants.

“This is our own war,” Gillani said. “This is a war which is against Pakistan.”

The four-month old coalition government in Islamabad has emphasised negotiations with militants and has characterised military action as a last resort. Pakistan, which has received more than $10 billion in US aid since 2001, has resisted suggestions that troops from the United States or other countries be allowed into the region.