A monitoring group says air strikes, believed to have been carried out by U.S.-led forces, hit Islamic State and other Islamist groups in eastern Syria on September 27.
The British-based Syrian Observatory for Human Rights said at least 31 blasts were heard in Raqqa province, where IS has its headquarters, adding that there were reports of casualties.
The coalition also hit IS targets in the town of Minbej, east of Syria's second city Aleppo, for the first time.
Also for the first time, warplanes struck the Al-Hammad area, east of the ancient town of Palmyra, in Homs province.
Observatory director Rami Abdel Rahman said the targets hit in Homs province were far from the frontline with forces loyal to President Bashar al-Assad, who control Syria's third-largest city of Homs.
The strikes also hit IS targets around the town of Tabqa, which houses an air base captured by IS last month, and around the mainly-Kurdish town of Kobane, near the border with Turkey.
A different jihadist group fighting in Syria, the al-Qaeda linked al-Nusra Front, has been hit by some of the air strikes and on September 27 the group threatened to retaliate against the countries carrying out those attacks.
Meanwhile, the British Ministry of Defense confirmed that British jet fighters have left a base in Cyprus for Iraq on their first mission in the campaign against the IS militant group.
Earlier, on September 26, the United States' top military officer said air strikes against Islamic State fighters in Syria have disrupted the militant group's command, control and logistics ability.
But General Martin Dempsey, chairman of the Joint Chiefs of Staff, told reporters that a ground force of up to 15,000 fighters would also be needed in Syria. He said the force should be drawn from Syria's moderate opposition.
Dempsey said he expected a "persistent and sustained" campaign against the militant group, which has seized a vast swath of Iraq and Syria.
According to Dempsey, Washington is also planning to train and arm 5,000 Syrian rebels as part of the effort.
The United States began a series of air strikes against IS targets in Iraq in August, and this week began attacks in Syria.
A senior U.S. defense official said the mission in Syria is now similar to U.S.-led air raids undertaken in Iraq, with "near continuous" combat flight operations against IS targets in Syria.
The Pentagon said air strikes had disrupted lucrative oil-pumping operations that have helped fund the militants.
Experts say black-market sales of oil from Syria and Iraq usually earn IS up to $3 million a day.
The coalition strikes in Syria are reported to have killed at least 140 jihadists as well as 13 civilians.
The U.S.-led coalition against the IS group widened on September 26 with Britain, Belgium, and Denmark approving plans to join air strikes in Iraq.
Britain's House of Commons voted by 524 deputies to 43 to back a motion authorizing air strikes in Iraq.
Denmark and Belgium have announced they will send seven and six F-16 fighter jets respectively to join the Iraq operation.
France has already joined the U.S.-led aerial campaign in Iraq.
About 40 countries, including several from the Middle East, have joined the anti-IS coalition.
But no European nation has yet agreed to join the United States and some Arab states in carrying out strikes in Syria.
With reporting by AFP, AP, Reuters, and BBC