The battle to retake Tabqa is seen as a vital strategic objective before the assault on Daesh's Syria stronghold of Raqqa.
The Syrian Democratic Forces (SDF), supported by the United States, captured a key district of the town of Tabqa from Daesh on Monday in a big step towards the capture of the country's largest dam.
Tabqa sits on the Euphrates River and on a strategic supply route about 55 kilometres (35 miles) west of Raqqa, the Syrian heart of Daesh's so-called caliphate.
In their drive for Raqqa, the SDF have captured more than 90 percent of Tabqa, but have not been able to fully clear Daesh out of the city or the adjacent dam.
The SDF is dominated by YPG, which Turkey considers an offshoot of the PKK. The PKK has been designated a terrorist organisation by Turkey, the EU and the US.
The SDF assault on Tabqa began after US-forces helped its fighters conduct an airborne and water crossing of the Euphrates in late March.
The battle for Tabqa is taking place in the backdrop of a "de-escalation zones" deal.
The multi-phase plan, signed last week in the Kazakh capital Astana, is one of the more ambitious efforts to end Syria's six-year conflict.
It provides for a ceasefire, rapid deliveries of humanitarian aid and the return of refugees after "de-escalation zones" are created across stretches of eight Syrian provinces.
The deal also calls for a continued fight against Daesh across Syria and to reduce violence in areas controlled by regime and rebel forces.
But the Syrian Observatory for Human Rights says the deal has not been entirely effective in achieving that goal.
Syrian regime forces advance in Hama
The Syrian regime forces seized control of the village of al Zalakiyat north of Hama on Sunday amid a heavy bombardment, the Observatory said.
Violence has raged in the countryside north of Hama for over a month, since rebels there launched an assault against regime forces that was quickly reversed and has now turned into an army push into areas the insurgents gained last year.
Under the "de-escalation zones" agreement, that took effect at midnight on Friday, fighting was intended to subside over six months in areas where violence between the regime forces and rebels have been most intense.