Air and missile strikes, thought to be carried out by U.S.-led forces, hit oilfields and Islamic State bases in the eastern Syria overnight and early Friday, a monitoring group said.
U.S. and Arab forces started bombing Islamic State militants in northern and eastern Syria on Tuesday. The United States has been bombing bases of the al Qaeda splinter group in Iraq since last month.
The air strikes early on Friday hit Islamic State bases and positions on the outskirts of the city of al-Mayadin in Deir al-Zor province, said the Britain-based Syrian Observatory for Human Rights, which monitors the conflict through a network of sources.
An earlier air strike hit the al-Tanak oilfield area in the province, while apparent missile strikes -- also thought to be carried out by U.S.-led forces -- hit the al-Quriyah area, also in Deir al-Zor, the monitoring group said.
Strikes also hit areas southeast of the city of Hasaka, close to Syria's border with Iraq. They targeted Islamic State, al Qaeda's Nusra Front and other Islamist militants, the Observatory said.
Deir al-Zor, which borders Iraq, is almost entirely controlled by Islamic State militants and was a major oil-producing province before Syria's conflict began more than three years ago.
Oil has been a top source of revenue for Islamic State militants, and air raids on Thursday targeted refineries controlled by the group. The strikes also have seemed to be intended to hamper Islamic State's ability to operate across the border with Iraq, where it also control territory.
The Observatory said there were casualties from the earlier strikes but did not give details.
NEW RECRUITS JOIN ISLAMIC STATE
More than 200 fighters have joined Islamic State in Syria's northern Aleppo province since U.S. President Barack Obama said the United States would strike the militant group in Syria, a monitoring group said on Friday.
At least 162 people joined the radical al Qaeda offshoot in northeast and eastern Aleppo in the week after Obama's speech on Sept. 10, said the Britain-based Syrian Observatory for Human Rights, which gathers information on the conflict.
Islamic State has put particular pressure on rival insurgent groups in this part of Aleppo.
An additional 73 men had joined the group on Sept. 23 and 24 in the northeast Aleppo countryside since the start of the strikes, the Observatory said, bringing the total number since Sept. 10 to at least 235.
"This means these people are not scared. Even if there are air strikes, they still join," said Rami Abdelrahman, who runs the Observatory.
He said the pace of recruitment in September was higher than average but below the surge in July, after Islamic State declared a caliphate in the territory it controlled in Syria and Iraq and called on Muslims to join a holy war.
Most of the new men came from al Qaeda's Syrian wing, the Nusra Front, and were mostly Syrian, the Observatory said. The men who joined in the week after Obama's speech included 15 nationalities, it added.
Islamic State recruited at a record pace in July, according to the Observatory, which counted at least 6,300 new members that month, a big expansion from earlier estimates suggesting the group numbered around 15,000. Around 1,000 of the new fighters were foreign, and the rest Syrian.
REUTERS