WASHINGTON — India-Pakistan relations could be one casualty of a bomb blast outside the Indian Embassy in Kabul yesterday that killed 41 people and injured more than 140.

While a Taliban spokesman denied responsibility for the deadliest attack in Afghanistan since the fall of the Taliban government in 2001, the Indian Ministry of External Affairs announced that it would send investigators to Pakistan and Afghanistan to probe the incident. The State Department said it is offering Afghanistan and India assistance in finding those responsible.

RELATED: Pakistani Leader Denies Role in Kabul Bombing | Afghan Official Suggests Pakistani Link to Attack

While Pakistan condemned the attack, a suspect is Inter-Services Intelligence, the country’s primary security agency, which, through its support of the Afghan Islamist resistance, was a key ally of America in the campaign to repel the Soviet army from Afghanistan in the 1980s.

Today the ISI is believed to have a number of cells at its middle and lower levels that are more loyal to the Taliban than to the government in Pakistan’s capital, Islamabad. The Afghan government in April blamed the ISI for coordinating a failed assassination attempt on President Karzai.

India, which lost four citizens in yesterday morning’s attack, has fought three wars with Pakistan since both nations broke away from the British Empire in 1947.

“It is impossible to look at that attack and not see the hand of the ISI behind it,” a fellow at the American Enterprise Institute, Christopher Griffin, said. “There are several indicators. Pakistan is unhappy with the growing Indian influence in Afghanistan. India has built consulates throughout the country, given $750 million in aid to Afghanistan, and is assertively supporting the government of President Karzai.”

Mr. Griffin said it would be difficult to prove that Pakistan had a hand in the operation, however, citing the ISI’s support for attacks in the disputed region of Kashmir through proxies.

Yesterday’s attack has the effect of undermining stability in Afghanistan and diminishing Indian influence in the country, he added.

A senior fellow at the Council on Foreign Relations and a former State Department South Asia specialist, Daniel Markey, said he was skeptical about any claims that the ISI was behind the operation.

“There are very good reasons why militants in the Taliban and other groups in Afghanistan would have motivation to hit the Indians,” he said. “They tend to see the Indians as an enemy. I don’t think you need the ISI piece of it to go there. I don’t think there is any way to confirm that, either. You are never going to see anything except for innuendo, which is based on the fact that Pakistan is unhappy with India’s presence in Afghanistan. That you would see this sort of tactic from the Pakistanis goes far beyond any evidence.”

A senior fellow and South Asia expert at the Brookings Institution, Stephen Cohen, said any number of groups or individuals could be behind the attack. “This could be someone working for a government security service or someone thinking they are working for a government security service,” he said. “There are hundreds of suspects.”

A spokesman for the Taliban, Zabiullah Mujahid, said his group was not responsible. “Whenever we do a suicide attack, we confirm it,” he said. “The Taliban did not do this one.”

The reaction from Washington was muted. The spokesman for the National Security Council, not President Bush or Secretary of State Rice, issued America’s statement on the attack.

“Extremists continue to show their disregard for all human life and their willingness to kill fellow Muslims as well as others,” Gordon Johndroe said. “The United States stands with the people of Afghanistan and India as we face this common enemy.”

Later, a spokesman for the State Department, Sean McCormack, said: “We condemn these attacks. And in the incident in Kabul, we have offered any assistance, not only to Afghan but also to Indian authorities, in terms of follow-up, determining who’s responsible for these attacks.”

Yesterday’s incident was the sixth major attack in the Afghan capital this year.

Over the last 12 months, fighting on the Afghan front has intensified as the insurgency in Iraq has receded. The two major American candidates for president, senators McCain and Obama, have pledged to send more American troops to Afghanistan and to urge NATO to send more troops, as well.