BEIRUT (Reuters) - Syrian soldiers clashed with Islamic State militants outside a government-controlled army airport on Friday, a British-based monitoring group said, part of a major escalation of fighting between the al Qaeda offshoot and the military.
The hardline Sunni militants have gained ground in Syria over the past five weeks, bolstered by equipment seized in a lightning offensive last month in neighbouring Iraq.
On Thursday, the group seized the Sha'ar oilfield, east of the central city of Homs, in what the Britain-based Syrian Observatory for Human Rights said was one of its bloodiest clashes with President Bashar al-Assad's forces.
On Friday, the death toll from the raid rose to 115, the Observatory said. The fate of 250 others was unknown, it said.
A video posted online on Thursday, purportedly of the battle site, showed armed men pacing through a barren desert space speaking in Arabic and German as they reviewed what appeared to be more than 50 bodies, many with gunshot wounds to the head, chest and legs. Some of the bodies appeared to be young men.
"Here lie two pigs," said one of the men, speaking German. At least two multiple-rocket launchers and other military vehicles were visible.
The Observatory, an anti-Assad group which tracks the violence through a network of contacts in Syria, said the government had sent reinforcements backed by helicopters to the nearby Hajjar oil field.
In Raqqa province, which borders Turkey, a woman - sentenced to death for adultery by the Islamic State - was stoned to death, the Observatory said. The report could not immediately be corroborated.
On Friday, fighting also broke out between Islamic State militants and government forces at the army airport in Deir al-Zor, one of the last major strategic locations in Deir al-Zor province not under the control of the Islamic State.
The Syrian army responded to the militants' offensive by bombing areas around the airport, which supplies its forces in the east of the country, the Observatory said. There were no details of casualties.
The fighting was just a few hundred metres (yards) from the airport, the Observatory's director Rami Abdurrahman said, noting that it would be tough for the Islamic State to overcome government forces there.
The Islamic State expelled rival rebels from Deir al-Zor city on Monday, tightening its hold on the eastern province bordering Iraq. [ID:nL6N0PP2YH]
Capturing most of Deir al-Zor province has helped the Islamic State link up territorial gains across Syria and Iraq, where it seized the northern city of Mosul in June. Last month it also declared an Islamic caliphate in territory it controls in both countries.
The group, previously known as the Islamic State in Iraq and the Levant, follows al Qaeda's hardline ideology but draws strength from foreign fighters, many with experience in Iraq.
(Reporting by Sylvia Westall and Alexander Dziadosz; Editing by Louise Ireland)