Islamic State militants retreating from Palmyra laid thousands of mines they planned to set off simultaneously as the army moved in, a Syrian officer says in the ancient city after its recapture.
The officer said on Saturday (local time) that main streets and side roads in Palmyra had been rigged with explosives weighing up to 50 kg.
More than 3000 had already been safely detonated since government forces, backed by Russian jets, retook the city last Sunday, he said.
He did not say why the Islamic State fighters failed to set off the explosives before pulling out, but his assertion echoed comments from Syria's antiquities chief, who said the militants intended to dynamite a greater area of the city's 2000-year-old ruins than they already had.
The officer, who did not give his name, said the bombs left behind were linked so they could go off together.
"All the government buildings are rigged in a network connected to the Daesh leadership headquarters," he said, using an Arabic acronym for Islamic State.
"The idea was that as we enter it would all go off at once, not just bomb by bomb. And there are a really huge number of bombs."
Parts of Palmyra have been cleared, including the road from Homs. But Syrian soldiers -- soon to be joined by Russian de-mining experts -- are still working on defusing or detonating explosives.
"We cannot leave them there. We are dealing with 90 percent of them by exploding them because they are buried firmly in the ground, cemented in the asphalt," the officer said.
Civilians, most of whom fled before Syrian and allied forces began the offensive, cannot return until de-mining is complete.
Residential areas have been damaged and traces of explosions could be seen on the ground.