The Obama administration said Thursday that Iran is helping al-Qaeda funnel cash and recruits into Pakistan for its international operations, the most serious U.S. allegation to date of Iranian aid to the terrorist group.

Documents filed by the Treasury Department accuse Iran of facilitating an al-Qaeda-run support network that transfers large amounts of cash from Middle East donors to al-Qaeda’s top leadership in Pakistan’s tribal region.

A Syrian national who directs the network has been allowed to operate in Iran since 2005, and senior Iranian officials know about money transfers and allow the movement of al-Qaeda foot soldiers through its territory, administration officials said.

New evidence cited

Although U.S. officials have repeatedly accused Iran of assisting al-Qaeda, links between the two have been difficult to prove. Al-Qaeda regards the Shiite denomination, the dominant branch of Islam in Iran, as heretical, and Iran has sought at times to crack down on the terrorist group, deporting some operatives and holding others under house arrest.

U.S. officials asserted that the alleged network offered new evidence of Iranian support. “By exposing Iran’s secret deal with al-Qaeda, allowing it to funnel funds and operatives through its territory, we are illuminating yet another aspect of Iran’s unmatched support for terrorism,” said David S. Cohen, the Treasury Department’s undersecretary for terrorism and financial intelligence.

The new allegations against Iran come as the administration is seeking to increase international pressure on the Islamic republic. The White House has successfully pushed for additional sanctions against Iranian companies while renewing accusations that the country’s leaders support militias inside Iraq that carry out attacks against U.S. forces.

On Thursday, Iran denied any links to terrorism. Alireza Miryousefi, a spokesman for Iran’s mission to the United Nations, accused U.S. officials of attempting to tarnish Iran’s reputation with “baseless allegations.”

“Iran itself has been a victim of acts of terrorism in the past which have resulted in the loss of hundreds of innocent Iranian lives,” Miryousefi said. “Iran has always opposed supporting and financing terrorist groups such as al-Qaeda.”

The allegations of a Iran-to-Pakistan network center on a Syrian operative, Ezedin Abdel Aziz Khalil. Khalil has directed the flow of cash and recruits from Persian Gulf states to Pakistan through Iran, according to U.S. officials and documents.

The Treasury Department imposed sanctions on Khalil and five other alleged operatives, including Atiyah Abd al-Rahman, a senior al-Qaeda leader on the Pakistani end of the pipeline. Rahman, a top spiritual adviser to al-Qaeda, was a longtime aide to Osama bin Laden, the al-Qaeda leader slain this year in Pakistan, and he once served as a bin Laden-appointed emissary to the Iranian government.

Individual operatives collected large amounts of cash, sometimes in the hundreds of thousands of dollars, and the money passed through Iraq by way of couriers or informal transfer systems known as hawalas, U.S. officials said. Much of the money was collected in Kuwait and Qatar, two countries that administration officials say have been relatively lax about stanching the flow of money from wealthy Arab donors to al-Qaeda.

“Kuwait and Qatar are not in the same league as the Saudis or the Emiratis when it comes to having the capacity or the will” to crack down on illegal money networks, said a senior U.S. official familiar with the case who insisted on anonymity in discussing sensitive diplomatic matters.

Al-Qaeda weakened

Many U.S. counterterrorism officials think that al-Qaeda has been weakened by the death of bin Laden and other top leaders, but the flow of money into the group’s coffers has allowed it to continue to operate, the official said. “Al-Qaeda is not destitute, but it is not flush,” he said. “Now is the time to be tightening the screws.”

Although Shiite-led Iran and Sunni-dominated al-Qaeda are theologically opposed, Iran’s ruling clerics have occasionally aided al-Qaeda, particularly in permitting its operatives to travel through Iranian territory. Army Gen. David H. Petraeus, the Obama administration’s new choice to head the CIA, told Congress last year that al-Qaeda was using Iran as a “key facilitation hub, where facilitators connect al-Qaeda’s senior leadership to regional affiliates.”

“And although Iranian authorities do periodically disrupt this network by detaining select al-Qaeda facilitators and operational planners, Tehran’s policy in this regard is often unpredictable,” Petraeus said in written testimony to the Senate Foreign Relations Committee.

Staff writer Greg Miller contributed to this report.