An air strike Thursday evening killed at least 35 civilians, including family members of Islamic State fighters, in al-Mayadin, a town held by the jihadists near Deir al-Zor in eastern Syria, a war monitor reported.
Two days of aerial bombardment in al-Mayadin have now killed a total of 50 people, the Britain-based Syrian Observatory for Human Rights monitoring group said.
A spokesman for the U.S.-led coalition fighting Islamic State told Reuters that its forces had conducted strikes near al-Mayadin on May 25 and 26 and were assessing the results.
Residents saw reconnaissance aircraft and warplanes circling the city at 7:25 p.m. (1625 GMT) before they fired missiles, which struck two buildings, one of which was a four-story block housing Syrian and Moroccan families of Islamic State fighters.
In Geneva on Friday, the U.N. human rights chief called on all air forces operating in Syria to take greater care to distinguish between legitimate military targets and civilians in their escalating air strikes especially in the northeast against Islamic State.
The rising toll of civilian deaths and injuries already caused by airstrikes in Deir-ez-Zor and Al-Raqqa suggests that insufficient precautions may have been taken in the attacks, U.N. High Commissioner for Human Rights Zeid Ra'ad al-Hussein said in a statement.
His spokesman Rupert Colville told a Geneva briefing: There are multiple air forces operating in this part of Syria, including the (U.S.-led) coalition, mainly the coalition. We also understand that there are Iraqi airplanes as well.
IS losing ground
Islamic State is losing ground in Syria and Iraq under assault from an array of sometimes rival forces in both countries. Many of its fighters who have retreated from other fronts are massing in Syria's Euphrates basin area.
The U.S.-led coalition says it is careful to avoid civilian casualties in air strikes and investigates any that are reported to have taken place.
Source: Voice of America