Activists say U.S.-led air strikes have targeted Syrian oil installations held by the militant Islamic State (IS) group overnight and early on September 25, killing nearly 20 people.
The latest strikes came on the third day of a U.S.-led air campaign and appeared to be aimed at one of the militants' main revenue sources.
The IS group captured most of Syria's largest oil fields earlier this year and is believed to be partly funding its operations by smuggling oil out and selling it on the black market.
The U.S. military estimates the refineries have generated as much as $2 million in daily revenue for IS.
The British-based Syrian Observatory for Human Rights and two local activist groups said at least four oil installations and three oil fields were hit around the town of Mayadeen in the eastern province of Deir el-Zour.
At least 14 militants were killed, said the observatory, which gathers information from a network of activists on the ground.
The observatory said another five people who lived near one of the refineries in the northeastern Hassakeh province were also killed, adding that they were likely the women and children of the militants.
Unconfirmed reports quoting local activists say that militants freed at least 150 people from a prison in their de facto capital of Raqqa in northeastern Syria, fearing more strikes.
Other strikes hit IS checkpoints, compounds, training grounds and vehicles throughout the territory they hold along the Euphrates River in northern and eastern Syria. Strikes hit near the Turkish and Iraqi borders.
The raids targeted Syrian military bases seized by the Islamic State group.
The observatory said other air strikes targeted the Al-Nusra Front, a Syrian Al-Qaeda affiliate that has fought the Islamic State, and which is one of the most powerful groups fighting to overthrow Syrian President Bashar Assad.
The observatory also reported air strikes near a northern Kurdish area that Islamic State militants have been attacking for nearly a week now, causing the flight of over 150,000 people to neighboring Turkey.
It was not immediately clear who was conducting the airstrikes southwest of the area known as Kobani, or Ayn Arab.
Kurdish officials said on September 25 that Peshmerga forces pushed back an advance by Islamic State fighters towards the town of Kobani in overnight clashes.
Meanwhile, security sources said that Syrian government troops recaptured the key rebel-held town of Adra, northeast of the capital Damascus on September 25.
The rebels captured Adra in December last year. It is strategically located on the northeastern entrance to Damascus, and has in the past been used as a launching pad for attacks on the edges of the capital.
With reporting by AP, Reuters, AFP, and the BBC