Officials from the FBI and Immigration and Customs Enforcement (search) were serving a search warrant Thursday on an Islamic center in Fairfax, Va., as part of a terrorism probe, four government officials told Fox News.

There are several parts to this Joint Terrorism Task Force (search) investigation into the Institute of Islamic and Arabic Sciences in America. The key part is a probe into the possibility of terrorism financing.

Another part is the search for evidence that people associated with the organization may be helping — and perhaps harboring — illegal aliens. The search warrant was "under court seal," which means it was not to be made public.

Officials said the investigation was still in the early stage, with no individual target as yet.

A message left at the Islamic center was not returned.

The Defense Department used to do business with the school — an arm of the Saudi government — to recruit chaplains to run Pentagon programs for Muslim soldiers. The institute is part of Saudi Arabia's state-run university system and is funded and controlled by the kingdom's Ministry of Higher Education.

According to the Wall Street Journal, the institute's published curriculum calls for studying "the ruinous effect" of Christian beliefs. Lecturers have included a cleric who congressional investigators say was a spiritual adviser to two of the Sept. 11 hijackers. And the Muslim-American activist who helped arrange for the institute to train Muslim lay leaders, Abdur Rahman Alamoudi (search), was indicted in October for taking from Libya money that prosecutors suspect was intended to finance terrorism.

The institute is described as "a non-profit educational and research institution. Among the various activities of the institute are teaching Arabic and Islamic courses, and undertaking research in Islamic studies."

Fox News' Anna Stolley contributed to this report.