BEIRUT - The US-backed Syrian Democratic Forces (SDF) launched an attack on an eastern district of Islamic State-held Raqqa and on a military base on the northern outskirts of the city on Tuesday, the Syrian Observatory for Human Rights said.
"It started today at dawn," Observatory Director Rami Abdulrahman told Reuters. SDF officials could not immediately be reached for comment.
"We declare today the start of the great battle to liberate the city of Raqa, the so-called capital of terrorism and terrorists," SDF spokesman Talal Sello told reporters in the village of Hazima, north of the city. He said the attack has been launched from the east, west and north of the city.
With air support from a US-led coalition, the SDF has spent months sealing off the jihadists in Raqa, the heart of their territory in war-ravaged Syria. The SDF has asked civilians inside the city to keep away from IS positions and from the front lines.
"With the international coalition's warplanes and the state-of-the-art weapons they provided to us, we will seize Raqa from Daesh," Sello told AFP, using an Arabic acronym for IS.
The United States began providing small arms to Kurdish fighters battling the Islamic State group in northern Syria last month.
Raqa is considered the last major bastion for IS in Syria.
The weapons include AK-47s and small-caliber machine guns.
President Donald Trump approved arming the fighters from the Kurdish Peoples' Protection Units (YPG).
As the SDF has drawn closer to the city, reports of civilian casualties in coalition air strikes have swelled.
On Monday, the Observatory said a coalition bombing raid killed 21 civilians as they tried to escape Raqa by dinghy on the Euphrates River.
The same route had been used by IS fighters, Abdel Rahman said.
More than 320,000 people have been killed and millions more have fled their homes since the civil war erupted in Syria in March 2011.