BEIRUT (AP) — Islamic State militants overran the famed archaeological site at Palmyra early on Thursday, just hours after seizing the central Syrian town, activists and officials said, raising concerns the extremists might destroy some of the priceless ruins as they have done in neighboring Iraq.

The Islamic State's capture of the town of Palmyra late Wednesday was a stunning triumph for the militant group, only days after it captured the strategic city of Ramadi in Iraq's largest Sunni province.

As IS took Palmyra, government forces collapsed in the face of the attacks and Syrian soldiers were seen fleeing the area, activists said. In Damascus, state TV acknowledged that pro-government forces had withdrawn from the town.

Rami Abdurrahman of the Britain-based Syrian Observatory for Human Rights said the extremists overrun the archaeological site, just to the southwest of the town itself, shortly after midnight Wednesday.

An activist in Homs who goes by the name of Bebars al-Talawy also said that IS now controls the ruins at Palmyra. Both activists said that the militants had not damaged the site so far.

The ruins at Palmyra are one of the world's most renowned historic sites and there were fears the extremists would destroy them as they did major archaeological sites in Iraq. The UNESCO world heritage site is famous for its 2,000-year-old towering Roman-era colonnades and other ruins and priceless artifacts. Before the war, thousands of tourists a year visited the remote desert outpost, a cherished landmark referred to by Syrians as the "Bride of the Desert."

Many Palmyra residents were fleeing the town toward the city of Homs and the capital, Damascus, according to Talal Barazi,

Barzai, the governor of the central province of Homs, which includes Palmyra, told The Associated Press that the Syrian army is now outside the town, from where it is targeting Islamic State reinforcements.

"We have not received any news about (the archaeological site's) destruction," Barazi said. "We hope that there will be no massacres in the city or damage to the ruins."

Palmyra has a population of some 65,000 people, according to Barazi. He added that 1,300 residents fled over the past days and more were trying to leave on Thursday.

In taking the town, IS also overran Palmyra's notorious Tadmur prison, where thousands of Syrian dissidents have been imprisoned and tortured over the years.

An amateur video posted online showed IS fighters setting a giant poster of President Bashar Assad, allegedly inside the prison in Palmyra, cheering as flames rose around them against the night sky.

The video and its location could not be independently verified but appeared genuine and corresponded to other AP reporting of the events.

Al-Talawy, the Homs activist, said the government had recently transferred thousands of detainees from the Palmyra prison to a jail near Damascus.

But he added that IS extremists freed some of those who were still inside by the time they captured the prison. He could not provide any definitive figures but there were believed to have been thousands prisoners still there.