Federal agents have raided the U.S. branch of a large Saudi-based charity, founded in Northern Virginia by a nephew of Osama bin Laden, in connection with a terrorism-related investigation, law enforcement sources said yesterday.

The raid Friday on the World Assembly of Muslim Youth (WAMY) in Alexandria was carried out by agents of the FBI, U.S. Bureau of Immigration and Customs Enforcement and the Joint Terrorism Task Force, the sources said.

In a statement last night, WAMY said that all of the office's files and computer hard drives were seized and that a volunteer WAMY board member was arrested on immigration charges.

Sources said the raid was part of an investigation into whether the group's operations around the world have financial and other ties to terrorists, but the scope of the probe could not be learned because the case is under court seal.

But in its statement, the Riyadh-based, tax-exempt charity strongly denied any terrorist ties and said the government had told them the probe is focused only on "immigration issues.'' Although acknowledging that bin Laden's nephew, Abdullah bin Laden, was involved in forming WAMY's U.S. branch in Northern Virginia, the group said people should not assume that means it has any terrorist connections.

"While we fully agree with you that Osama Bin Laden is a terrorist and his acts have been condemned by the whole world including members of the Bin Laden family, we as a nation should be careful not to find 'guilt by association,' " said the statement, released through Asim Ghafoor, a spokesman for the group.

Prosecutors have alleged in previous court documents that WAMY espoused hatred of Jews and portrayed people who murdered Israelis as heroes. But the WAMY statement compared the group's activities to the YMCA, saying it focuses on "youth education, youth development and serving the Muslim community.''

About 50 agents participated in Friday's raid, the WAMY statement added.

U.S.-Saudi relations have been particularly sensitive since the Sept. 11, 2001, terrorist attacks: 15 of the 19 hijackers were from Saudi Arabia. The two governments are now cooperating on many fronts in the war on terror, especially since a series of attacks by Islamic militants with al Qaeda ties shook the desert kingdom in May 2003.

WAMY's name came up in another recent terrorism-related case in Northern Virginia: the investigation into a network of Islamic charities operating in Herndon and elsewhere in the region. The probe involved allegations of tax fraud and other improprieties. The charities strongly deny wrongdoing.

During last year's case against Soliman S. Biheiri, the only person convicted as an outgrowth of that investigation, prosecutors filed documents saying that Biheiri's company, BMI Inc., had managed money for Abdullah bin Laden. The documents said Abdullah bin Laden incorporated WAMY's U.S. branch in Falls Church in 1992, became president and was listed on the organization's tax forms until at least 1998. The branch is now in Alexandria.

An affidavit signed by Customs Senior Special Agent David C. Kane contends that a WAMY publication lists people who have attacked Israelis, including a man who killed 14 people by driving a bus off a cliff, as "Heroes from Palestine.''

Kane writes that a section of that document, titled "Animosity Toward the Jews,'' lists reasons for Muslims to hate Jews, including, "The Jews are humanity's enemies: they foment immorality in this world.''

The affidavit also lays out what it calls ties between WAMY and the Islamic Resistance Movement, or Hamas, which has been designated a terrorist organization by the U.S. government.