BEIRUT - Air strikes hit Islamic State and other Islamist groups in eastern Syria early on Saturday, a monitoring group said, as a U.S.-led coalition seeks to turn the tide against the militants who have captured swathes of Syria and northern Iraq.
The Britain-based Syrian Observatory for Human Rights said at least 31 explosions were heard in the province of Raqqa, a stronghold of Islamic State, and casualties were reported.
It said warplanes also struck areas east of the desert town of Palmyra in Homs province and hit several IS checkpoints around the Kurdish town of Kobani close to the Turkish border.
Later on Saturday, a Reuters witness saw two British fighter jets leaving a Royal Air Force base in Cyprus, a day after the British parliament authorized air strikes on Iraq.
The U.S.-led air campaign has yet to stop the advance of the Islamic State fighters on the town of Kobani, also known as Ayn al-Arab, which has been under attack for at least 10 days. The assault has sent 140,000 refugees across the frontier since last week in the biggest such exodus in three and a half years of civil war.
"Today, they (IS fighters) have made advances on the western side of the town," Rami Abdelrahman of the Observatory said.
The United States is leading a military coalition including some Gulf and European nations to stop the advance of Islamic State, which swept across northern Iraq in June. The group has proclaimed a "caliphate" ruling over all Muslims, slaughtered prisoners and ordered Shi'ites and non-Muslims to convert or die.
The campaign has brought Washington back to the battlefield of Iraq that it left in 2011 and into Syria for the first time after avoiding involvement in a war that began the same year.
Militant groups in the region and websites commonly used by their supporters did not immediately mention any attacks on Saturday.
The targets of the air strikes on Saturday included several military bases occupied by IS including Tabqa military airport, where many members of the group were killed, the Observatory said, without giving a figure.
Syria's government, which in the past accused its opponents of being Western agents trying to topple President Bashar al-Assad, has not objected to the air strikes that began on Tuesday and said it was informed by Washington before the air campaign began.
It too has carried out air strikes across the country, including in the east and its ground forces have recaptured the town of Adra, northeast of Damascus, tightening Assad's grip on territory around the capital.
But Russia questioned the legality of U.S. and Arab air strikes in Syria because they were carried out without the approval of Damascus, Moscow's ally.
"It's very important that such cooperation with Syrian authorities is established, even now that it's an accomplished fact," Russian Foreign Minister Sergei Lavrov told reporters on the sidelines of the U.N. General Assembly in New York on Friday.
Until this week France was the only Western country to answer President Barack Obama's call to join the campaign. Since Monday, Australia and the Netherlands have also joined. On Friday, Germany expressed support for the mission, although it will not send aircraft of its own.
Lawmakers in Britain and Belgium have now approved taking part in the air campaign. Turkey said its troops could be used to help set up a secure zone in Syria if there was an international agreement to establish such a haven for refugees fleeing IS fighters.
General Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, said this week's strikes in Syria had disrupted Islamic State's command, control and logistics capabilities.
But he said a Western-backed opposition force of 12,000 to 15,000 would be needed to retake areas of eastern Syria controlled by the militants. (Reuters)