THE HAGUE, Netherlands -- Three Dutch marines are being held by authorities in Libya after they were captured by forces loyal to Moammar Gadhafi while trying to rescue Dutch workers, a Defense Ministry spokesman said Thursday.

The three were surrounded by armed men and captured Sunday after landing near Sirte in a Lynx helicopter that was on board the navy ship HMS Tromp, which is anchored off the Libyan coast to help evacuations from the conflict torn country, spokesman Otte Beeksma told The Associated Press.

Dutch officials are in "intensive negotiations" with Gadhafi's government to secure the marines' release, he said.

"We have also been in contact with the crewmen involved," Beeksma said. "They are doing well under the circumstances and we hope they will be released as quickly as possible."

Asked if the Dutch government considered the marines hostages, Beeksma said, "they are being held by Libyan authorities."

Two people the marines were trying to rescue also were captured but have since been released and have left Libya.

The identities of the marines were not released.

News of the marines' detention by Gadhafi came a day after anti-government rebels fought off forces loyal to Gadhafi in a fierce battle for Brega, a strategic oil facility 460 miles (740 kilometers) east of Gadhafi's stronghold in Tripoli.

Gadhafi's crackdown has been the harshest in the Arab world to the wave of anti-government protests sweeping across parts of the Middle East and North Africa. His forces are regrouping in an attempt to regain territories now controlled by opponents of his regime.

Later Thursday, the prosecutor of the International Criminal Court, Luis Moreno-Ocampo, is scheduled to announce he is opening an investigation into possible crimes against humanity committed in Libya.