One of several Pakistani students rounded up by British authorities on allegations of terrorism — later dropped — described his detention as "mental torture" after returning to his native country Thursday.

The case has strained relations between Britain and Pakistan, especially after British authorities failed to produce enough evidence to back up the terror charges but insisted on deporting the students anyway.

"I fail to understand still why they kept us under detention," Tariq ur Rehman, apparently the first to be sent home, told reporters in brief comments at the Islamabad airport. "We were accused of being Islamic extremists."

Twelve people, most of them Pakistanis in Britain on student visas, were arrested in dramatic daytime operations across England on April 8. The arrests were rushed in part because one of the country's top counterterrorism officers inadvertently exposed details of the operation to a photographer outside the prime minister's office.

Authorities' failure to charge the men was an embarrassment for Britain and Prime Minister Gordon Brown, who said at the time of the arrests that police had disrupted "a very big terrorist plot."

Britain has said it wants to deport all but one of the men on national security grounds, prompting protests from Islamabad. Britain's Home Office has refused to say what the men are accused of or how long they might be held before deportation.

"I think the mental torture is worse than physical torture," Rehman told reporters. He declined to say if he would sue Britain. It was not immediately clear what he had been studying there.

Britain's embassy in Islamabad said Rehman had agreed to voluntary deportation.

British High Commission spokeswoman Jennifer Wilkes said it might issue a statement on Rehman's case later Thursday.

Some of the students have lawyers and are fighting to stay and resume their studies in Britain. Several students' families in Pakistan have begged British officials to allow them to finish their degrees, saying their futures are at stake.

Pakistan Foreign Ministry spokesman Abdul Basit, while noting Rehman had returned to Pakistan voluntarily, said his government stood behind the students who were fighting to stay in Britain.

"We still want our students to be released. We still want them to be allowed to continue their studies," he said. "We support them."

Britain has a large population of Muslims of Pakistani descent and is a popular destination for Pakistani students who want to study abroad. The detainees' case has caused outrage among British Muslims, with supporters holding vigils and protests.