The US-led coalition published aerial photos it said showed the Tabqa dam had not been bombed
US-backed Syrian fighters have paused their offensive near the Tabqa dam so engineers can do any work necessary to ensure it continues to function.
The Syrian Democratic Forces alliance is battling Islamic State militants for control of the structure, which is on the River Euphrates west of Raqqa.
On Sunday, the US-led coalition against IS denied claims by the group that air strikes had damaged the dam.
However, there have been reports that the dam has been put out of service.
The UN has warned that if the dam were to collapse, it could lead to flooding on a “massive scale” across Raqqa province and as far downstream as Deir al-Zour with “catastrophic humanitarian consequences”.
Why is the Tabqa dam important?
Stretching 4.5km (2.8 miles) across the eastern end of Lake Assad, the dam is Syria’s largest.
IS captured the dam in 2014, giving it control of a vital reservoir and a hydroelectric power station that supplies large parts of the country.
The coalition also says the dam has been used by hundreds of IS foreign fighters as a headquarters, as a prison for high-profile hostages, as a training location and to plot attacks outside Syria.
The offensive on the dam is part of a wider SDF offensive aimed at also driving IS militants from the nearby town of Tabqa and its airbase, which fell on Sunday.
Is the dam at imminent risk of collapse?
On Sunday, IS said coalition air strikes had locked the dam’s gates, causing water levels to rise dangerously behind the structure. The dam might collapse “at any moment”, it warned.
Civilians living downstream in Raqqa – the de facto capital of the “caliphate” proclaimed by IS in June 2014 – were told to evacuate and many began leaving their homes, according to the activist group Raqqa is Being Slaughtered Sile.
Later, the jihadist group reportedly sent cars around Raqqa with loudspeakers, telling people the dam was intact and they had no need to evacuate.
The coalition meanwhile insisted the dam had not been targeted by air strikes and had not been structurally damaged “to our knowledge”.
The SDF was in control of a spillway to the north that could be “used to alleviate pressure on the dam if need be”, it added.
Why is the offensive being paused?
The coalition stressed that it was “taking every precaution to ensure the integrity”, including by avoiding the use of high-explosive munitions in air strikes.
But on Monday afternoon, the SDF announced that it was halting its operations around the dam for several hours to “ensure the safety” of the structure.
The decision came following a request from the dam’s administrators, without specifying whether they were part of the Syrian government or IS, it said.
A source at the dam told AFP news agency that it was forced out of service on Sunday after the power station was damaged, and that the engineers would “assess the level of damage and repair what is needed”.
What is the SDF?
Kurdish, Arab, Turkmen and Armenian militias opposed to IS established the umbrella group in northern Syria in October 2015.
Since then, its 50,000 fighters have seized about 6,000 sq km (2,300 sq miles) of territory with the help of coalition air strikes and special forces personnel.
Although the coalition estimates that about 60% of the SDF’s fighters are Arabs, the force is led by the Kurdish Popular Protection Units (YPG) militia.
This has caused trouble for the US with a major ally, Turkey’s government. It considers the YPG an extension of the Kurdistan Workers’ Party (PKK), which is banned in Turkey and is designated a terrorist group by the US and EU.
In response, the US has pledged to support only Arab groups within the SDF.