US-backed Syrian fighters on Monday paused their offensive for a key dam held by ISIL to allow a technical team to enter the complex, a spokeswoman said.

There have been fears about the integrity of the dam after fighting in the area forced it out of service on Sunday, following earlier United Nations warnings that a collapse would be "catastrophic".

With air support from the US-led coalition against Islamic State of Iraq and the Levant (ISIL), the Syrian Democratic Forces (SDF) are fighting to seize the town of Tabqa and the adjacent dam on the Euphrates, as part of their battle to take the hardline group's self-declared capital of Raqqa.

"To ensure the integrity of the Tabqa dam ... we have decided to stop operations for four hours beginning at 1:00pm (1100 GMT)," SDF spokeswoman Jihan Sheikh Ahmed said in a statement.

"This is to allow a team of engineers to enter the dam and carry out their work," she added.

The decision followed a request by the Syrian government's water authority.

The director of the Syrian government's General Authority of Euphrates Dam, which formerly operated the huge project, blamed US strikes in the past two days for disrupting internal control systems and putting the dam out of service.

The dam, Syria's largest, stretches 4.5km across the Euphrates. ISIL captured the dam and a nearby airbase, lying about 40km upstream from Raqqa, at the height of its expansion in Syria and Iraq in 2014.

"There was growing concern over the weekend [about the dam's potential collapse]. In fact, ISIL was driving around nearby villages and towns warning them that there was a danger of flooding," said Al Jazeera's Alan Fisher, reporting from Beirut.

ISIL issued warnings through its propaganda agency Amaq on Sunday that the dam could collapse "at any moment".

READ MORE: US-backed forces 'capture' Tabqa airbase from ISIL

The dam was forced out of service on Sunday after its power station was damaged, a source at the dam told the AFP news agency.

The activist group Raqqa is Being Slaughtered Silently reported that ISIL had ordered Raqqa residents to evacuate the city.

The UN has warned that damage to the dam "could lead to massive scale flooding across Raqqa and as far away as Deir Az Zor" province downstream to the southeast with "catastrophic humanitarian implications".

The source at the dam told AFP on Monday that a technical team "will assess the level of damage and repair what is needed so that the dam can resume its operations, after it was put out of service yesterday".

The US-led coalition said Monday it was "taking every precaution" to ensure the structure's integrity.

The SDF has denied the dam was damaged, and said military operations around it were being conducted "slowly and with precision".

Fighting is almost certain to resume after the four-hour window is up, “unless engineers come out and say there is a real problem here and that they have to fix it because thousands of lives could be at risk”, said Al Jazeera's Fisher.

Hundreds of families fled Tabqa to the relative safety of outlying areas as coalition air strikes intensified in the past few days, according to former residents in touch with relatives.

The SDF alliance announced on Sunday that it had seized a majority of the nearby Tabqa airbase from ISIL.

Earlier this week, US forces airlifted SDF fighters and US advisers behind ISIL lines to allow them to launch the Tabqa assault.

"This is a part of the approach… the [US-led coalition's] assault on Raqqa, and gaining key strategic points, including the nearby airfield and the dam, all become part of the operation," said Fisher.

The SDF launched its offensive for Raqqa city in November, seizing around two thirds of the surrounding province, according to the UK-based Syrian Observatory for Human Rights.

At their closest point, they are just 8km from the city, to the northeast.