The Associated Press

ZAGREB, Croatia — The prime minister promised an investigation Friday into Croatia's worst firefighting tragedy, in which six men were killed and seven badly injured when they were trapped battling a fierce forest blaze.

The group — including volunteers aged 17 and 18 — was encircled by flames Thursday when the wind suddenly changed course while they were fighting the fire on Kornat island, national firefighting chief Mladen Jurin said.

Police said eight men had been detained on suspicion of arson. The state-run news agency HINA said the eight were seasonal construction and tourist workers who were allegedly filmed setting the fire by a German tourist.

The fire was brought under control early Friday.

The victims had been among 23 firefighters initially sent to fight the Kornat blaze. At one point, the 13 went to confront flames that threatened homes on the island, but were trapped when the fire changed course and surrounded them.

Women and children were jumping into the sea as the fire approached their homes, firefighter Nikola Kurkut told Croatian daily Vecernji list.

Kurkut, who joined the overnight rescue effort, told the newspaper that victims "looked horrible." The injured firefighters were taken by a helicopter to a hospital; the dead were to be removed from the site of the fire later Friday.

Five of the seven wounded had life-threatening injuries, and were transferred overnight to two clinics in the capital, Zagreb, doctors said. Burns covered 85-90 percent of their bodies.

Prime Minister Ivo Sanader visited the injured early Friday in the first clinic in the coastal city of Zadar, saying it was the "biggest tragedy in Croatian firefighting."

"The government insists on a thorough investigation," he said. If it was arson, the government wanted the "perpetrators to be identified and harshly punished," he said.

President Stipe Mesic demanded an inquiry into the firefighting commanders, saying that they "should have left a way for their retreat."

The chief Croatian firefighter, Jurin, defended his colleagues and said the incident was part "of the risks of our job."

The county governor declared a seven-day mourning period, and said the dead included a 17-year-old and two 18-year-old members of the local volunteering firefighting brigade. Others were professional firefighters. The injured also included both volunteers and professionals.

Kornat is the biggest island in the archipelago of Kornati, off central Croatia in the Adriatic Sea. Dozens of small islands, mostly uninhabited and surrounded by clear blue water, are popular with tourists.

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Croatia has battled a record number of 1,500 fires this summer, mostly only in forests. The only other casualty recorded this year was a firefighter who died Wednesday after falling ill while putting out fires on another island.