A Muslim scholar resigned his appointment to the University of Notre Dame (search) on Tuesday four months after the Bush administration revoked the scholar's work visa before he could take up his teaching position.

"I'm abandoning the idea of moving to the United States," Tariq Ramadan (search) told The Associated Press from Geneva. "I want to maintain my dignity."

Ramadan notified the university on Monday, citing the stress on him and his family from the uncertainty of their situation, said R. Scott Appleby, director of Notre Dame's Kroc Institute for International Peace Studies (search).

Ramadan, a Swiss citizen, was barred from working in the United States in August just days before he was to begin teaching at Notre Dame. The Department of Homeland Security cited security concerns but released no specifics. Ramadan's work visa was issued in May.

Ramadan said Tuesday there is nothing in his past to justify the ban and demanded that U.S. authorities give details of its investigation of him in order to clear him of the "untrue and humiliating" claims that he was barred because of ties to terrorism.

"This is an obstacle to academic freedom of expression," he said.

He took a year's unpaid leave from his posts in Switzerland in order to work at Notre Dame and is now out of a job. "I don't have any new plans for the moment," he said.

He had been paid by Notre Dame until he resigned, said Matt Storin, a university spokesman.

The revocation of his visa sparked protests from at least four U.S. scholars' groups, led a United Nations-sponsored institution to issue an academic freedom alert and inspired appeals on Ramadan's behalf from some Jewish groups.

Many who have rallied in support of Ramadan believe the scholar's sharp criticism of Israel, the war in Iraq and U.S. policy in the Mideast was the reason for the revocation.

At the time, the Department of Homeland Security (search) said the decision was based on "public safety or national security interests" and pointed to federal law applying to aliens who have used a "position of prominence ... to endorse or espouse terrorist activity."

State Department spokesman Richard Boucher said the case had been under review, but that Ramadan's resignation would end the review process. He declined further comment.

The scholar's studies focus on showing how Islamic values are compatible with those of secular European society, and he has gained a popular following among European Muslims.

In October, he applied again for a work visa. The school said it never received word on the status of that application.

"Faculty and students at Notre Dame and at other U.S. universities were looking forward to engaging him productively on a variety of issues central to our times," Appleby said. "Such dialogue, we believe, is an essential requirement to a deeper understanding of the complexity of the Muslim world."