The Obama administration told Congress today that Iran’s state-owned oil company is linked to a military unit sanctioned for weapons proliferation, terrorism and human-rights abuses.

Treasury Secretary Timothy F. Geithner was required by Congress to prepare the report, which determined that the National Iranian Oil Co., known as NIOC, is “an agent or affiliate” of Iran’s Islamic Revolutionary Guard Corps, according to two letters to lawmakers from the Treasury Department. The finding exposes foreign financial institutions that deal with the company to U.S. sanctions.

Under a law signed Aug. 10, Congress gave the Obama administration until today to determine whether the oil and tanker companies were controlled by the elite unit. Lawmakers are seeking to deny funding to the Guard, known as the IRGC, as part of an array of sanctions intended to pressure Iranian Supreme Leader Ali Khamenei to halt his country’s suspected pursuit of nuclear-weapons capability.