Satellite images released by the U.N. training and research agency UNITAR in Geneva showed the main temple building and a row of columns had been flattened. The explosion Sunday was the militants` second attack on the world-renowned ruins in a week.

As local activists and antiquities experts scrambled Monday to determine what had happened, all agreed the blast had damaged the best-preserved structure of the temple, a stone building that included the altar.

Some experts had clung to optimism by saying the extent of the damage was still unclear, while residents and activists said reports indicated severe damage.

Maamoun Abdulkarim, the director of Syria`s antiquities department, had said he thought the main building had remained standing, nonetheless calling any damage a loss.

"It`s not a political battle, but this is a cultural battle, and everybody should participate in defending this heritage, this civilization," he said.

The damage to the nearly 2,000-year-old Temple of Baal came just a week after the militants, who have held the Palmyra ruins and the modern city with the same name for three months, destroyed another important ancient building there, the nearby Temple of Baalshamin.

The Temple of Baal was an even grander structure, with a towering altar building on a platform of large stone blocks at the center of a larger plaza encircled by columns and partial walls.

"It is not as huge as the damage at Baalshamin," Abdulkarim said.

Khaled al-Homsi, an antigovernment activist and Palmyra native who recently fled to Turkey but remains in close contact with residents of the city, accused Abdulkarim of trying to play down the damage. Homsi said that much of the structure had been knocked down, including a portico of eight columns just outside its walls and the altar inside.

Homsi`s uncle, Khalid al-Asaad, 83, a former antiquities director in Palmyra, was killed by the militants two weeks ago, his body suspended from a traffic light.

Consecrated in A.D. 32 to the Semitic god Baal, the temple - also known as the Temple of Bel, a different transliteration of the god`s name - is considered one of the most important sites in Palmyra. It was a relatively intact example of the fusion of Middle Eastern, Greek and Roman influences.

In modern times, the Temple of Baal has also been a cultural touchstone for Syrians. It has been a backdrop for concerts in the annual Palmyra Music Festival, as the ancient amphitheater has been more recently for Islamic State executions.

The ancient city of Palmyra, which stands in the desert about 150 miles northeast of Damascus, is a UNESCO World Heritage site.

The Islamic State has widely publicized images of its fighters blowing up tombs and destroying statues that it considers blasphemous under its extremist interpretation of Islam. Archaeologists and antiquities experts consider the losses to be irreparable, leading some to feel, as Abdulkarim said last week, "very weak, very pessimistic."

On Monday, he added that among Syria`s many archaeological treasures, the Temple of Baal had special significance for him.

"I visited the temple during the crisis," he said, "and I took many pictures with my daughter, which is something I rarely do."

He added, "It was an honor to stand in front of this great place."

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