STOCKHOLM, Sweden (AP) - A U.S. envoy on Thursday defended the detention of suspected terrorists and Taliban fighters at a U.S. naval base in Cuba and warned that al-Qaida terrorists are planning "massive attacks" against civilians.

In an opinion article in the daily newspaper Dagens Nyheter, the U.S. ambassador-at-large for war crimes, Pierre-Richard Prosper, said detainees being held at Guantanamo Bay were being treated according to the Geneva Conventions on prisoners of war, although the United States considers them "unlawful combatants."

Prosper, visiting Stockholm on a tour of European capitals, also said the war on terrorism and the al-Qaida terrorist network was not over.

"These terrorists continue to attack allied forces in Afghanistan, carry out attacks in Bali and other places and they plan to carry out massive attacks of an unprecedented scale against civilian targets," he said. He did not provide evidence.

Prosper said a Swedish citizen being detained at Guantanamo wouldn't be released because he isn't cooperating with authorities.

"In our judgment, based on his earlier actions and his unwillingness to cooperate, he still constitutes a security risk," he said.

Sweden has called on the United States to present evidence against Mehdi-Muhammed Ghezali or release him.

Hans Dahlgren, a spokesman for the Foreign Ministry, said he reiterated Sweden's view in a meeting with Prosper on Thursday. He declined to comment further on the meeting.

On a visit to Denmark on Monday, Prosper said that some detainees at Guantanamo Bay have asserted they would commit acts of terrorism if released.

About 650 detainees from 43 countries are being held at the U.S. naval base on suspicion of links to al-Qaida or Afghanistan's former Taliban regime.