BEIRUT (Reuters) - The U.S.-led coalition struck Islamic State fighters crossing the Euphrates to support their comrades in Raqqa on the first day of the battle to drive the jihadists from the city, the coalition's spokesman said on Tuesday.
The Syrian Democratic Forces (SDF), a coalition-backed alliance of Kurdish and Arab militias, on Tuesday began to assault Raqqa, the Syrian capital of Islamic State's self-declared caliphate.
Over months of fighting to the north, west and east of Raqqa, the SDF has with coalition air, artillery, intelligence and logistics support, isolated it against the Euphrates.
As the SDF began to push into districts of Raqqa city on Tuesday, the coalition used both air and artillery strikes to hit Islamic State (IS) defences, its spokesman Colonel Ryan Dillon said by phone.
Between Monday afternoon and Tuesday afternoon, the coalition struck IS tactical units, destroyed 19 boats, 12 fighting positions, eight vehicles and a weapons store, he said.
Although IS still controls the south bank of the Euphrates opposite Raqqa, coalition airstrikes in recent months have destroyed the bridges connecting it to the city.
"This is not the first time we have struck barges and water craft that have moved across the river to support the operations that ISIS is doing in and around Raqqa," Dillon said, referring to IS.
The 19 boats hit on Tuesday carried fighters and equipment, he added.
Coalition air strikes have killed many civilians in Raqqa and the other IS-held towns along the Euphrates river valley, war monitors and human rights groups have said. The coalition says it tries hard to avoid civilian casualties and investigates any that are reported.
The battle to defeat IS in Mosul has already lasted months and the coalition expects the jihadists to use equally fierce tactics to defend their next-largest possession, Dillon said.
The coalition estimates that 3,000-4,000 IS fighters are in Raqqa and about 200,000 civilians.
"They have had three years to establish their defences there. We expect a fight very similar to what we've seen in Mosul," he said, while adding that Raqqa is a much smaller city.
The militants' "weapon of choice" is the armoured car bomb, driven by a suicide attacker at defensive positions or concentrations of forces, Dillon said. Protective plates welded to such vehicles stop light arms fire aimed at killing the driver or exploding the bomb prematurely.
"We have clearly seen some of the tactics that they use when it comes to using human shields or herding civilians," he added.
The SDF has encouraged people to leave Raqqa to escape that fate, he said, and has established screening sites at forward battle lines to separate civilians from disguised fighters.
Beyond Raqqa, IS still holds the eastern part of the Euphrates valley running to the Iraqi border and swathes of desert to the south.
In an earlier statement on Tuesday, the coalition commanding general Lt. Gen Stephen Townsend was quoted as saying that even after Raqqa "there will still be a lot of hard fighting ahead".
Reporting By Angus McDowall; Editing by Angus MacSwan