Warplanes from the US-led coalition have bombed oil installations and other facilities in territory controlled by the Islamic State in Iraq and the Levant (ISIL) in eastern Syria for a second consecutive day, activists said.
The strikes reportedly hit two oil areas in Deir ez-Zour province on Friday, a day after the US and its Arab allies attacked a dozen makeshift oil producing facilities in the same area near Syria's border with Iraq.
The US Central Command said three air strikes south and southeast of Deir ez-Zour destroyed four ISIL tanks and damaged another.
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The Britain-based Syrian Observatory for Human Rights said the strikes overnight and early on Friday hit the Tink oil field as well as the Qouriyeh oil-producing area in Deir ez-Zour.
The raids aim to cripple one of ISIL's primary sources of cash - black market oil sales that the US says earn up to $2m a day.
The Observatory and another activist collective, the Local Coordination Committees, also reported strikes on the town of Mayadeen, including on the ISIL headquarters.
Deir ez-Zour, which borders Iraq, is almost entirely controlled by ISIL and was a major oil-producing province before Syria's conflict began more than three years ago.
Strikes also hit areas southeast of the city of Hasakah, close to the Iraqi border. They targeted ISIL, al-Qaeda's Syrian branch the Nusra Front and other fighters, the Observatory said.
Al Jazeera's Zeina Khodr, following the conflict from neighbouring Beirut, said the strikes on ISIL would undoubtedly weaken the group, which controls large parts of Syria and Iraq.
"They'll be on the defensive, they won't be able to expand the territory they control. It will be hard for fighters to move from one area to another, especially in large convoys.
"But now ISIL is adapting to the air strikes, hiding among civilians. It will be very hard to defeat the group."
Reports from the ground said dozens of fighters, from ISIL and the Nusra Front, as well as some civilians, have been killed since the US-led coalition began its bombing campaign in Syria early on Tuesday.
Hundreds of civilians and soldiers have been killed in ISIL's fight to take control of territory in the east and north of Syria and in neighbouring Iraq. The widely-feared group has attacked minorities in both countries and drawn international outrage after the beheading of two American journalists and a British aid worker.
But the foreign intervention has been met with mixed reactions among Syrians, with the political opposition saying the US and its allies should also strike the regime of President Bashar al-Assad.
Protests against the strikes were held in several towns on Friday, some in support of the Nusra Front.
The air campaign is led by the US, supported by Saudi Arabia, the UAE, Qatar, Bahrain, Jordan and France.
Source: Al Jazeera and agencies