Senior members of the rebel force proclaimed the start of the campaign this weekend in Ain Issa, a town about 35 miles north of Raqqa - halfway between the larger city and the Turkish border.
USA officials have acknowledged that ousting IS from Raqqa poses tougher political challenges than the offensive on Mosul, and have suggested the initial stage would involve isolating the city before any forces try to move in.
A United States military official told CNN that SDF forces would begin by working positions east of Raqqa to shut down the so-called "back door" escape out of the city and to cut off ISIS supply routes between Raqqa and Mosul.
"When it comes to Raqqa we want a force that ultimately liberates Raqqa that is primarily from the local area, Arabs from the area, and so we have trained many of these fighters and that force will continue to grow as we get to the subsequent phases of the campaign", McGurk told reporters.
The offensive was announced Sunday by the Syria Democratic Forces, a Kurdish-led group with Arab fighters that is backed by USA air power.
Iraq's Hezbollah Brigades, one of the main Shiite militias taking part in the government-led push to drive IS from Mosul, said Wednesday its men had taken control of a highway linking Mosul and Raqqa, severing a key supply route between the two militant strongholds. Sello also said that Washington has agreed Turkey will play no role in the battle to capture Daesh's Syrian bastion Raqqa.
SDF forces seized control of six villages and farms, the Britain-based Syrian Observatory for Human Rights said. The U.S. considers the group to be the most effective force against IS, but Turkey views it as a terrorist organization linked to a Kurdish group outlawed by the government in Ankara. It also reported strong activity by USA -led coalition warplanes and airstrikes that hit IS positions. The Royal Air Force "will support the Raqqa operation as it develops", Defense Secretary Michael Fallon said.
They have deployed waves of suicide vehicle bombs, as well as mortar attacks, roadside bombs and sniper fire against the advancing troops, and officers say they have also left behind fighters among residents of districts taken over by the army.
Early voting ends Saturday, turnout strong so far
Courthouse officials say today's voter turnout was very successful and encourage everyone to vote so their voice can be heard. And black voters' share of early voters has declined in Florida since 2012, despite an increased early voting period.
The commander of anti-IS coalition forces, Lt. Gen. Stephen Townsend, said last week that American intelligence has detected signs that Islamic State attacks against Western target are being plotted from Raqqa, adding urgency to coalition plans to encircle and eventually assault the city.
The Raqqa-based Syrian activist group known as Raqqa is Being Slaughtered Silently also reported the clashes south of Ein Issa.
Turkey's defense minister last week suggested that instead of the Kurds, Turkish-backed forces can present an "alternative".
Dominated by the powerful Kurdish People's Protection Units (YPG), the SDF has in recent months flushed IS out of swathes of territory in northern Syria, including the flashpoint town of Manbij in August.
France has long suspected that IS planned last year's Paris attacks in Raqqa.
In a statement, the US-led task force carrying out Operation Inherent Resolve to defeat ISIS acknowledged the offensive had been launched and said it continued its support the SDF.
"The facts are these: The only force that is capable on any near-term timeline is the Syrian Democratic Forces, of which the YPG are a significant portion", he said.
- No charges against Clinton after new email review
- Andre Roberson, Thunder Held Extension Talks But Unable To Agree On Deal
- People, what's going on with this election?
- Campaigning for Clinton, Obama reflects on his own legacy
- Man City could have beaten Barca more emphatically - Ilkay Gundogan
- VW quits world rally in cost-cutting move
- Sergio Aguero would deliver the Premier League says Ian Wright
- Syria Kurds announce start of campaign to retake Raqqa
- Michigan And Penn State Rightly Reject Friday Night Games
- U.S. government launching effort to stop Russian Federation from hacking election