At least 38 Islamic State (IS) group militants were killed in US-led coalition air strikes this week near Syria's ancient city of Palmyra, a monitor said on Saturday.

The militants retook Palmyra in central Syria on 11 December, just eight months after the army, backed by Russia, drove them out.

On Thursday, US-led coalition aircraft destroyed heavy weaponry seized by the militants when they retook the city, the coalition said.

#Palmyra will be retaken by the Syrian army. But what must be retaken is the border with #Turkey, where the terrorists cross to and from. — Dr Marcus Papadopoulos (@DrMarcusP) December 17, 2016

Palmyra is a UNESCO World Heritage site, and its recapture by IS gave the militants a propaganda boost as they face assaults on two of their key strongholds - Raqqa in Syria and Iraq's second city Mosul.

The US-led coalition battling IS said on Friday it destroyed 14 tanks, an air defense artillery system and other weaponry near the city. The strikes, which the military said in a statement took place on Thursday, followed a warning from the US military that it could strike weapons it believed posed a danger to the US-led coalition in the region, Reuters said.

Among the Russian weaponry IS captured around Palmyra were thought to be modern surface-to-air missiles, or SAMs, giving militants the potential capability to shoot down aircraft, a coalition official told AFP.

The Syrian Observatory for Human Rights, a monitoring group based in Britain, said that "at least 38 IS members were killed in the air strikes".

The strikes, near the Tiyas military air base northeast of Palmyra, helped regime forces gain some ground west of the fabled city, said the Observatory.