SYDNEY, Australia — A stateless Kurdish-Iranian asylum-seeker detained by the Australian government won the country’s highest-paying literary prize on Thursday. But he could not attend the festivities to accept the award.

Behrouz Boochani, a writer, journalist and filmmaker who has been held in offshore detention on Manus Island in Papua New Guinea for more than five years, won the 2019 Victorian Prize for Literature for his book, “No Friend but the Mountains.”

The prestigious award, selected from a short list of winners in other categories, grants the winning author 125,000 Australian dollars (about $90,000) and counts the country’s most prominent writers among its recipients.

Mr. Boochani fled Iran after the police there arrested several of his journalist colleagues and raided his office. After the Australian Navy intercepted his boat as he was trying to reach the country, he was sent to Manus Island in 2013.

Since then, he has written articles for numerous local and international outlets. His book, which recounts his experiences in detention, was written over five years through WhatsApp texts in Farsi to his translator, Omid Tofighian, who accepted the award in his stead on Thursday night in Melbourne.

Reached by telephone on Friday, Mr. Boochani said the award felt paradoxical.

“I am happy because it is a great achievement for me and all of the refugees, and it is a victory against this system,” he said. But the suffering he has witnessed on Manus Island deeply saddened him.

“Hundreds of people have been separated from their families for years,” he said, adding, “We are living in a place worse than a prison.”

He wrote the book through WhatsApp because at the time, detention center guards would search detainees’ rooms and seize their phones. “I was worried that if they attacked my room they would take my property,” he said.

Under Australia’s migration policy, asylum seekers who try to enter by sea are barred from entering the country. Since 2013, more than 3,000 refugees and asylum seekers have been sent to Australia’s offshore detention centers on the Republic of Nauru and Manus Island.

The government has defended the policy as an effective deterrent against smugglers, but global human rights activists have strongly condemned it.

In 2017, the Australian government closed the Manus Island center and moved asylum seekers there to alternative accommodations. Some refugees have since been resettled in the United States, but hundreds of people like Mr. Boochani remain in limbo.

[Read more: The New York Times went inside the detention camp on Manus Island.]

“It’s ironic that a book writing about the harrowing reality of our government’s punitive offshore detention policy is celebrated by winning such a prestigious award,” said Jana Favero, the director of advocacy and campaigns at the Asylum Seeker Resource Center.

While Mr. Boochani’s work deserved the award, she said, “it has come at the cost of his freedom.”

Typically, only Australian citizens or permanent residents are eligible for the award. But an exception was made in Mr. Boochani‘s case because judges considered his story an Australia story, said Michael Williams, the director of the Wheeler Center, a literary institution that administers the award on behalf of the state government.

“We canvassed the critical and broader literary reception of the book, and we made our decision on that basis,” Mr. Williams said. “This is an extraordinary literary work that is an indelible contribution to Australian publishing and storytelling.”

Though Mr. Boochani could not accept his award in person at the ceremony on Thursday night, the writer had a prerecorded message for the attendees.

“I believe that literature has the potential to make change and challenge structures of power,” he said in the message. “Literature has the power to give us freedom.”