BEIRUT (AP) — At least 15 people were killed in an airstrike in eastern Syria on Wednesday, activists said, in the second attack in three days reported to kill civilians in the Islamic State-held Euphrates River valley.

Two Syrian monitoring groups, Deir Ezzor 24 and Justice For Life, said the weapons were dropped on the village of Doblan by an unidentified jet. Russian, Syrian, and U.S.-led coalition aircraft are all known to operate in the area.

Cluster bombs are designed to spread small bomblets across a wide area, but many fail to explode, endangering civilians long after the fighting has ended.

Omar Abou Layla, the head of Deir Ezzor 24, said 15 bodies, including those of women and children, were recovered in the village. He said residents expect to find many more killed.

Ali Rahbe, of Justice For Life, said local informants counted at least 35 dead in the village, which is between the IS strongholds of al-Mayadeen and Boukamal.

The Britain-based Syrian Observatory for Human Rights put the initial toll at 30 dead.

At least 57 people were killed in an airstrike on an IS-run jail in the Euphrates River Valley on Monday. Activists said that airstrike was carried out by the U.S.-led coalition. The coalition said it was looking into the reports.

Most of the victims were prisoners held on charges of religious infractions, such as failing to observe the Ramadan fast, said Rahbe. The Observatory said 42 civilians were killed.

Though the IS group is on the retreat, it still holds approximately 250 kilometers (155 miles) of territory along the Euphrates River in Syria, which has come under immense pressure as rival U.S.-backed Syrian Kurdish forces and Russian- and Iranian-backed Syrian government forces race for control of the resource-rich region.

Monitoring groups warn that civilians are under attack. A U.N. commission of inquiry called the civilian death toll of the U.S.-backed campaign for Raqqa "staggering." The Observatory says 231 civilians have been killed in coalition airstrikes on IS territory in eastern Syria in the last three months.

The top U.S. envoy for the international coalition against the Islamic State group met with members of a local council expected to administer Raqqa after IS forces are driven from the city.

A member of the Raqqa Civil Council, Abdullah el-Erian, told the Kurdish-run ANHA news agency, that Brett McGurk's visit Wednesday is an "important message" as the U.S- backed fight to seize Raqqa continues. The two-hour meeting took place in Ayn Issa, a town about 30 miles north of Raqqa city, where the council is based.

A U.S. State Department official said McGurk visits Iraq and Syria often to discuss humanitarian and stabilization assistance, and to "coordinate between our military and civilian initiatives, as well as post-liberation governance for areas liberated" from IS.

"As the Coalition's campaign to liberate Raqqa accelerates, we are in regular contact with coalition partners from across the globe and on the ground in Syria," the official said on condition of anonymity in line with regulations.

Another council member, Omar Alloush, said the publicized visit was to reaffirm the coalition's support for the stability of the liberated areas in Raqqa, including clearing land mines, and rehabilitating schools and power plants. Alloush said the council, now in charge of large swathes of liberated parts of the province, is also seeking international financial support as it prepares to replace IS.

"The people of Raqqa have paid dearly because of IS," Alloush, who is also a member of the Syrian Democratic Council, the political arm of the Kurdish-led forces.

The fight for Raqqa began in earnest in early June, as Kurdish-led forces, backed by airstrikes from the international coalition, slowly advanced on several neighborhoods of the city considered the de-facto capital of the militant group.

The local council was formed in April, including Arab and Kurdish local leaders, and has been assuming its duties to administer liberated areas in the province.

Also Wednesday, Syrian government forces pushed on with their assault against rebels holed up in the northeast corner of capital and its suburbs, with a barrage of air and artillery strikes on the already devastated neighborhoods of Jobar and Ein Terma. Years of air strikes and heavy weapons fire have largely reduced the neighborhoods to rubble, according to new footage from the government's military media.

Turkey's military meanwhile said it returned fire after an attack by Syrian Kurdish forces.

A statement Wednesday said the People's Protection Units, or YPG, fired on Turkish territory overnight with anti-aircraft weapons from Syria's Afrin region. Turkish artillery units returned fire, destroying the "detected targets."

The YPG is the main component of the Syrian Democratic Forces, a U.S.-backed militia that is battling the Islamic State group in the extremists' de facto capital, Raqqa. Turkey views the YPG as an extension of the Kurdish insurgency raging in its southeast.

Turkey was angered by a U.S. decision last month to arm the Syrian Kurds, fearing the weapons will end up in the hands of Kurdish rebels in Turkey.

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Associated Press writers Suzan Frazer in Ankara, Turkey and Sarah El Deeb in Beirut contributed to this report.