Assailants attacked a convoy of buses transporting oil workers on Friday in an area of eastern Syria where the terrorist group Islamic State has been active, killing at least 10 people, according to state media outlets and groups that monitor the ongoing conflict in the country.
No group immediately claimed responsibility for the attack, which was in an area controlled by the Syrian government. But Islamic State has increased its attacks in eastern Syria over the past year, according to monitoring groups.
Islamic State lost the last territory in its self-proclaimed caliphate in parts of Syria and Iraq three years ago, but has managed to maintain sleeper cells in Syria. It regularly attacks targets including the Syrian government and U.S.-backed Kurdish fighters. The United States maintains a military presence in areas of eastern Syria.
Friday’s attack came one day after the Pentagon’s Central Command, which oversees American troops in Syria, said the United States and its partners had killed 466 Islamic State operatives in Syria this year and at least 220 more in neighboring Iraq.
“ISIS always, always tries to prove to its supporters and members that they are still present and that they can reach any point they want,” said Omar Abu Layla, executive director of Deir Ezzor 24, a news and analysis organization that focuses on Syria’s eastern province of Deir al Zour. “This is a clear message from the group to the group.”
The attack began when an explosive device detonated, targeting three buses carrying the workers to the al-Taym oil field in Deir al Zour Province. The assailants then opened fire at the buses, according to the Syrian Observatory for Human Rights, a monitoring group based in Britain. The observatory reported that 12 workers were killed, though state media outlets put the toll at 10.
Islamic State attacks have often targeted buses, but usually ones transporting soldiers, Mr. Abu Layla said.
He added that another reason behind the attack could be to further inflame tensions between the government of President Bashar al-Assad, which has clawed back control over most of the country after more than a decade of war, and the U.S. military, which maintains a number of bases in eastern Syria.
The oil field the workers were heading to is under the control of the Syrian government, which controls only some of the country’s oil and natural gas fields. Those sitting east of the Euphrates River are held by the U.S.-backed and Kurdish-led Syrian Democratic Forces, a group that controls much of northeast Syria.
Though the complicated and multisided Syrian war has transformed into a low-level conflict, there are occasional flare-ups with airstrikes and guerrilla attacks. The Syrian Observatory for Human Rights said that nearly 450 people had been killed in conflict this year in the desert areas in the center and east of Syria, where many of Islamic State’s sleeper cells are believed to be based.
This month, the U.S. military said it carried out two raids against the Islamic State in eastern Syria, killing or capturing operatives.
The raids “reaffirm Centcom’s steadfast commitment to the region and the enduring defeat of ISIS,” Gen. Michael E. Kurilla, the head of the U.S. Central Command, said in a statement this month. “The capture of these ISIS operatives will disrupt the terrorist organization’s ability to further plot and carry out destabilizing attacks.”
The Central Command report released on Thursday said that in Syria, U.S. forces had carried out 14 unilateral attacks against the Islamic State this year, along with another 108 in conjunction with their partners. In Iraq, American forces and their partners in the Iraqi security forces carried out 191 operations against the group.
The Syrian Observatory for Human Rights said more than 160 Islamic State members were killed by Russian airstrikes on the group’s desert hide-outs this year. And more than 260 government soldiers and pro-government militiamen were killed in 103 attacks by the Islamic State.
Syria’s oil and mineral resources minister, Bassam Tohme, said the country was suffering from an oil crisis and blamed terrorist groups and “the American occupation” for cutting off the available oil needed to secure the minimum needs of Syrians, according to Syrian state media outlets.