Islamic State militants attacked an oil and gas field in Syria Tuesday, killing at least 30 pro-government soldiers and security guards.
The group launched its assault on the Shaer field late Tuesday and fighting raged for much of the night.
“IS managed to control parts of the field,” the Syrian Observatory for Human Rights said.
A number of militants were also killed, although an exact count has not been released yet.
UK-based Syrian Observatory said fighting picked up again on Wednesday morning.
The Syrian army bombed the area near the field in Homs province.
Pro-government Syrian news sources confirmed the IS attack and said the group took control of two wells and a hill.
Army troops and the National Defense Forces have launched a counter-attack to retake control over the field, Syrian newspaper Al-Watan said.
In July, IS staged an assault in the same region that killed 270 people including soldiers and pro-regime troops.
The majority of the victims were executed at gun point, Agence France-Presse said.
IS relies on oil and gas produced in Iraq and Syria to fund its military operations.
The extremist group collects an estimated $1 million per day from oil and gas sales.
IS sells products processed at its refineries on the black market and to smugglers who then sell the product on the gray market in Turkey, Iran and Jordan.
Some of the oil is also sold to the Syrian government.
Most of the transactions are paid for in cash, making it difficult to track the deals or stop them, Bloomberg said.
Last week, President Obama threatened to impose sanctions on anyone purchasing oil or gas from IS.