The United States and its partners carried out at least 50 air strikes on Islamic State targets in the Syrian provinces of Raqqa and Deir al-Zor on Tuesday, while the al Qaeda-linked Nusra Front was also hit by air strikes in northwest Syria, a group monitoring the war in Syria said.
"There are tens of wounded and dead," Rami Abdulrahman, head of the Syrian Observatory for Human Rights, told Reuters by phone. The Observatory, which gathers information from a network of activists on the ground, said at least 20 Islamic State fighters were killed in the air strikes. He also said Nusra Front positions had been struck in the provinces of Idlib and Aleppo in northwest Syria.
The United States and several Gulf Arab allies have launched air and missile strikes on Islamic State targets in Syria, US officials said, opening a new, far more complicated front in the battle against the militants.
"I can confirm that US military and partner nation forces are undertaking military action against (Islamic State) terrorists in Syria using a mix of fighter, bomber and Tomahawk Land Attack Missiles," Rear Admiral John Kirby, Pentagon press secretary, said in a statement on Monday.
"Given that these operations are ongoing, we are not in a position to provide additional details at this time."
A US official, speaking on condition of anonymity, said that Saudi Arabia, the United Arab Emirates, Jordan and Bahrain were involved although their exact roles in the military action were unclear. Qatar played a supporting role in the air strikes, the official said.
Another official said at least one US ship had launched the surface-to-surface Tomahawk missiles. Armed US drones were also used in the attacks.
The United States has been building a coalition to combat Islamic State, an extremist Sunni Muslim force that has seized large expanses of territory in Iraq and Syria and proclaimed a caliphate erasing borders in the heart of the Middle East.
US Secretary of State John Kerry traveled to New York at the weekend, ahead of the start of United Nations General Assembly meetings, for talks with counterparts from Arab and European allies to discuss U.S. plans to defeat the Islamic State and hear their views on how they might participate.
On Monday, he met Saudi Foreign Minister Saud al-Faisal and British Foreign Secretary Philip Hammond, and participated in a meeting of more than a dozen countries, including Arab Gulf States, on the conflict in Libya.
A senior administration official said US plans "to expand our efforts to defeat (Islamic State) were discussed without specifics" during meetings but declined to elaborate.
The addition of Arab allies was seen as crucial for the credibility of the American-led campaign. US allies in the Middle East are skeptical of how far Washington will commit to a conflict in which nearly every country in the region has a stake, set against the backdrop of Islam's 1,300-year-old rift between Sunnis and Shi'ites.
Several Arab states have powerful air forces, including Saudi Arabia and the United Arab Emirates. Saudi Arabia has also already agreed to host US training of Syrian opposition fighters.
But many Gulf Arab states have been reluctant to be seen aggressively joining the US campaign, fearing in some cases reprisals by extremists or forces loyal to the Syrian government.
The strikes took place hours before Obama goes to New York for the UN General Assembly where he will try to rally more nations behind his drive to aggressively take on Islamic State.
Obama had shied away from getting involved in Syria's civil war a year ago, seeing no positive outcome for the United States, but the rise of Islamic State and the beheading of two American captives forced him to change course.
General Lloyd Austin, commander of the US military's Central Command, made the decision to conduct the strikes under authorization granted to him by Obama, Kirby said.