Residents have been told to leave Raqqa by Islamic State following warnings that a nearby dam could collapse.
The activist-run Raqqa Is Being Slaughtered Silently group said IS militants used loudspeakers on Sunday to tell people that the Taqba dam upstream on the Euphrates River had been weakened by US-led coalition airstrikes.
Water levels at the dam, which is about 25 miles west of Raqqa, were said to be rising behind the dam and IS has told residents that the airstrikes were preventing maintenance.
There was confusion, however, as the group later reported that IS militants had changed their minds and telling civilians not to leave the city.
The group said IS, which has held Raqqa since January 2014, was deliberately "spreading hearsay and contradiction".
It described the situation as "chaos", adding that the city had run out of electricity, water, gas and kerosene.
The UK-based Syrian Observatory for Human Rights confirmed the dam is out of service. Both groups use residents of Raqqa to smuggle information out of the city.
In January, the UN said damage to the dam could "lead to massive scale flooding across Raqqa and as far away as Deir Ezzor" province to the southeast.
A coalition of forces is closing in on IS's self-proclaimed capital, with Syrian President Bashar al Assad saying earlier in March that his forces were very close to taking the city .
A western-backed militia alliance, the Syrian Democratic Forces, is also advancing towards the city.
The YPG, Kurdish fighters who are part of this coalition, took control of Tabqa military airport to the west of Raqqa city on Sunday night.
IS took the airport from government troops in August 2014 and killed up to 200 government soldiers in a massacre there.
Meanwhile, a Syrian opposition group called on the coalition to stop targeting residential areas in and around the city for airstrikes.
The Syrian National Coalition, which is taking part in UN talks in Geneva, said that it was "increasingly concerned" about civilian casualties.
The SNC said it believed coalition forces were behind an airstrike that killed at least 30 civilians who had been sheltering in a school just outside Raqqa on 21 March.
The coalition is investigating this.
The Syrian Observatory for Human Rights said coalition airstrikes have killed 89 civilians in Raqqa province in the past week.