The Obama administration accused Iran on Thursday of facilitating an al-Qaeda pipeline that routes cash and recruits across Iranian territory into Pakistan.

The alleged Iran-to-Pakistan network, as described in documents filed by the Treasury Department, would represent the most significant known link between the Iranian government and al-Qaeda, which regards Iran’s brand of Shiite Islam as heretical. Iran formerly held key members of the terrorist group under house arrest.

The Treasury documents accuse Iran of knowingly permitting an al-Qaeda operative to run a sprawling international support network for the terrorist group on Iranian soil. The operative, Ezedin Abdel Aziz Khalil, allegedly has moved large sums of Middle East cash through Iran through couriers, while also delivering al-Qaeda recruits across the border into Pakistan, U.S. officials said. Khalil has been working in Iran since 2005 and has ties with Iranian government officials, they said.

“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 department imposed sanctions on Khalil and five other individuals alleged to participate in the network. Most of the money is collected elsewhere in the Middle East — particularly in Kuwait and Qatar — and ultimately is delivered to Atiyah Abd al-Rahman, a top spiritual adviser to al-Qaeda and a long-time aid to former al-Qaeda leader Osama bin Laden, U.S. officials said. Rahman, a Libyan, once served as a bin-Laden appointed emissary to the Iranian government.

While Shiite-led Iran and the Sunni-dominated al-Qaeda are theologically opposed, Iran’s ruling clerics have occasionally aided al-Qaeda, particularly in permitting the travel of its operatives through Iranian territory. Several U.S. officials recently have accused Iran of increasing its aid to al-Qaeda. 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 last March.