The FBI has subpoenaed records for dozens of bank accounts belonging to the Saudi embassy, in an unprecedented move that has strained relations with a close ally in the war on terrorism.

The move is part of an investigation into whether any of the $US300 million ($A415 million) the Saudi embassy spends in the United States each year ends up in the hands of Muslim extremists, US and Saudi officials said.

This year officials from the two nations established a joint taskforce to track terrorist financing in Saudi Arabia.

Although many Saudi entities have been investigated in the past, US officials said this was the first investigation to directly probe Saudi Government funds.

The probe, approved by the National Security Council working group on terrorist financing at the request of several congressional leaders, focuses on the financial activities of the Islamic and cultural affairs office of the embassy as well as the activities of Saudi consulates around the US, officials said.

The subpoenas outraged Saudi officials, who believe they were unnecessary...