Sardar Ahmad, a Canadian doctor from Afghanistan, was stopped at the U.S. border and was held for five hours for questioning before ultimately being denied entry into the country, the Sarnia Observer reported.

Ahmad was born in Afghanistan but left more than a decade ago when he received a Fulbright scholarship and moved to the United States. In 2007, he moved to Canada and later became a citizen there. Ahmad made a trip to Michigan on Friday after realizing his Nexus card had been revoked. The Nexus program offers expedited border crossing between Canada and the U.S. for pre-approved individuals.

When he arrived at the border crossing at Blue Water Bridge, where he explained the situation to border officials, Ahmad's keys were taken away and he was held and questioned for over five hours about his life prior to leaving Afghanistan.

He said he was asked about his "tribe" and the name of his "tribe chief" and whether he had seen "a lot of gunmen" growing up in Afghanistan.When Ahmad asked border officials to make a call to his clinic to cancel his patients he was told he could not touch the phone.

"It was frustrating for me because I was worried, I was scared, I didn't know what was going to happen next," he said. "You never know. They could put you in jail. You could lose your career – everything – all overnight."

Ahmad's detention comes amid ongoing controversy over President Donald Trump's proposed travel ban, barring people from seven majority-Muslim countries from entering the U.S., including Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen. The original order was nixed by the ninth Circuit Court of Appeals earlier this month, but Trump is expected to introduce another order soon.

It remains unclear why Ahmad was stopped. U.S. Customs and Border Protection said they could not comment on an individual case, citing privacy concerns. In an email to the Sarnia Observer, the agency wrote that it is "committed to the fair, impartial and respectful treatment of all members of the trade and traveling public."

"The United States has been and continues to be a welcoming nation," the spokesperson added. Ahmad has no interest in returning to the U.S. after being detained last week.

"I was telling [the U.S. border agents], 'I don't have to go here,'” he told the Observer. "'I live in the most beautiful country in the world.'"