BEIRUT -- U.S.-backed forces captured a strategically important air base from the Islamic State in northern Syria on Sunday in the first major victory for the forces since the U.S. airlifted them behind enemy lines last week.
The Syrian Kurdish-led Syrian Democratic Forces announced that they had captured the Tabqa air base 28 miles west of Raqqa, the Islamic State militant group's self-declared capital.
The U.S., which has provided substantial air and ground support, ferried hundreds of Syrian Democratic Forces members, as well as U.S. military advisers and U.S. artillery, behind Islamic State lines last week.
The airlift was a major development in the Syrian Democratic Forces' multifront campaign to bear down on Raqqa. The forces are within 6 miles of Raqqa from the north. The offensive comes as U.S.-backed forces in neighboring Iraq press their assault to seize Mosul, that country's last major city still held by the Islamic State.
Syria's Tabqa air base was captured by Islamic State militants from the Syrian government in August 2014. Shortly afterward, the group announced that it had killed about 200 government soldiers at the base. The mass killing was recorded and distributed on video over social media.
The Syrian Observatory for Human Rights, a monitoring group, also reported the Syrian Democratic Forces' advance.
Meanwhile, there were conflicting reports over whether civilians had begun evacuating Raqqa because of concerns over the stability of the nearby Tabqa Dam.
The militants said U.S.-led coalition airstrikes had locked up the dam's gates, causing the water level behind it to rise. The activist group Raqqa is Being Slaughtered Silently reported that the Islamic State had ordered Raqqa residents to evacuate. Tabqa Dam is 25 miles upstream of Raqqa on the Euphrates River.
U.S.-led coalition forces said they were not aware of any structural damage and that they had not targeted the dam.
Syrian Kurdish forces were in control of a spillway north of the dam that "can be used to alleviate pressure on the dam if need be," the coalition said in a letter to The Associated Press.
The Observatory said there were no evacuations happening from Raqqa, as did the activist-run Raqqa 24 media center.
Raqqa 24 said engineers employed by the militants had restored power to the dam's gates and that the structure was functioning normally.
The reports from Raqqa came as a leading Syrian opposition group called on the U.S.-led coalition to stop targeting residential areas in and around the city.
The Syrian National Coalition said in a statement that it was "increasingly concerned" about civilian casualties in the campaign against the extremist group. The exiled opposition coalition is taking part in United Nations-mediated talks in Geneva aimed at ending the country's civil war.
The coalition said it believed its forces were behind an airstrike that killed dozens of civilians sheltering in a school in the countryside outside Raqqa on Tuesday. The coalition has said it is investigating.
The U.S. has provided substantial air and ground support to the Syrian Democratic Forces, who are closing in on Raqqa as well as the Tabqa Dam.
The Observatory said coalition airstrikes had killed 89 civilians in Raqqa province in the past week, including 35 at the school in the village of Mansoura.
Hospitals targeted
Separately, a medical-relief advocacy group said more than 100 hospitals in Syria were hit by Syrian or Russian airstrikes last year. The group urged the fortification of medical facilities by adding reinforced concrete or blast-resistant windows.
In a 90-page report released Saturday, the International Union of Medical Care and Relief Organizations also pointed to an "alarming scarcity" of specialized care and supplies.
The report says all 107 hospitals surveyed in December in seven regions were hit at least once by "direct or indirect airstrikes" last year -- some as many as 25 times.
Three-quarters of hospitals surveyed were called "makeshift hospitals," as they were housed in buildings not initially designed to provide medical care, because real hospitals were either destroyed or made inoperable.
The International Union of Medical Care and Relief Organizations said all parties knew that those sites were makeshift hospitals.
Information for this article was contributed by staff members of The Associated Press.
A Section on 03/27/2017