BEIRUT (Reuters) - Islamic State seized more territory from Syrian government forces near the ancient city of Palmyra on Friday in fierce clashes that raged for a second day, the Syrian Observatory for Human Rights monitoring group said.

The jihadists launched an attack late on Thursday in which they captured grain silos northeast of Palmyra and have since taken at least partial control of oil and gas fields to its northwest.

Dozens of Syrian troops have been killed in the fighting, the British-based Observatory, which tracks the war using sources on the ground, said.

Syrian warplanes were carrying out air raids in the area in an effort to take back positions lost.

The fighting was some of the fiercest in the area since the Syrian army recaptured Palmyra after nearly two years in March, driving out the ultra-hardline militants who had destroyed large parts of the city’s UNESCO World Heritage ruins.

Islamic State has been on the back foot in both Syria and Iraq since late last year, losing much of its territory in both countries as well as some of its most senior figures, killed in air strikes.

The group took advantage of chaos during Syria’s civil war to seize territory there and in Iraq in the summer of 2014.

Syria’s civil war pits President Bashar al-Assad, backed by Iran, Russia and Shi’ite militias against mostly Sunni rebels.