AMMAN - Islamic State said on Tuesday it had downed a Syrian army helicopter in a desert area of central Syria where heavy fighting is going on, the militant group and a monitor said.

Amaq, a news agency associated with Islamic State, said the helicopter was shot down near in the Palmyra desert between Homs and Palmyra city.

The Syrian army has not commented on the report but had earlier said its war planes pounded Islamic State defences in the area and hit their convoys in the vicinity of the Shaer gas field, north of Huweisis, which the militants took over last Thursday.  The militants were also disrupting army supply lines and attacking the Mahr and Jazal gas fields, in an area which contains the country's largest gas reserves and facilities that once generated much of its electricity needs. The hardline militants, who were routed from Palmyra when the Syrian army backed by heavy Russian air power retook the ancient city in March, have staged a comeback in the area in the past two weeks. The British-based Syrian Observatory for Human Rights confirmed the militants were gaining new ground. It said that on Tuesday they seized a deserted military barracks 10 km (7 miles) north of the Syrian military's T4 airport, near where the helicopter was reportedly downed.

Amaq said earlier on Tuesday militants had taken over two checkpoints near the airport, killing at least 20 soldiers and seizing artillery and heavy armour.