The most intensive barrage of air strikes launched against Islamic State (Isis) since the US fight against the terror group began last month thundered into northern Syria until after dawn on Tuesday, heralding a new phase of a war that Sunni regional powers have vowed to help lead.

Large explosions were reported in the group’s stronghold of Raqqa, in eastern Syria, as well as in Idlib province. There were unconfirmed reports that attacks had also taken place near Deir Azzor and western Aleppo.



A Pentagon statement said the 14 strikes against Isis targets were carried out with Bahrain, Jordan, Saudi Arabia, the United Arab Emirates and Qatar. Jordan confirmed it its airforce had “destroyed a number of targets that belong to some terrorist groups that sought to commit terror acts inside Jordan” without making explicit reference to Syria.



Raqqa was among the targets of the operation, which began in the early hours of Tuesday morning local time. The head of the Syrian Observatory for Human Rights, Rami Abdulrahman, told Reuters by telephone in Beirut that the air strikes hit checkpoints in Raqqa city and surrounding areas. Dozens of Isis fighters were killed or wounded in the attacks, he said.

Buildings that had been used openly as Isis command centres in Raqqa were destroyed. However, they had long been evacuated as momentum built towards the attacks, and their occupants had melted into the streets of the city, which the middle of last year became the first Syrian city to fall completely outside the control of the regime.

Fighter jets, bomber aircraft, drones and Tomahawk missiles were used in an operation the Pentagon press secretary, Rear Admiral John Kirby, described as “ongoing”. The US military’s Central Command in Tampa, Florida, said 47 missiles were fired from the USS Arleigh Burke and USS Philippine Sea operating from international waters. It said all aircraft returned safely.



Rear Adm. John Kirby (@PentagonPresSec) US military & partner nation forces have begun striking ISIL targets in Syria using mix of fighters, bombers and Tomahawk missiles.

The US state department confirmed its ambassador to the UN, Samantha Power, gave her Syrian counterpart an advance indication of likely military attacks against Isis in the country - but strongly denied any military coordination.



“We warned Syria not to engage US aircraft,” said Jen Psaki, the state department’s spokeswoman, in a statement. ‘We did not request the regime’s permission. We did not coordinate our actions with the Syrian government. We did not provide advance notification to the Syrians at a military level, or give any indication of our timing on specific targets.”

At least eight explosions targeted a second group, known as Khorasan, near Idlib, which US officials described as “a network of seasoned al-Qaida veterans” plotting against US and western interests from inside Syria.



Khorasan has its origins in the mountains of Pakistan and Afghanistan and is little known in northern Syria, where the Isis leadership, drawn mainly from Iraq, has increasingly held sway over the past year.

The Syrian Observatory for Human Rights claimed that a third group, the al-Nusra front, an al-Qaida branch that has fought Isis, was also hit. This has not been confirmed by the US.



The president of the Syrian Opposition Coalition, Hadi al Bahra, said the strikes were necessary. “We have called for air strikes such as those that commenced tonight with a heavy heart and deep concern, as these strikes begin in our own homeland. We insist that utmost care is taken to avoid civilian casualties. Our people have been suffering at the hands of Isis for over a year.”



Kirby said the strikes were ordered by army general Lloyd Austin, the commander of US forces in the Middle East and South Asia, “under authorisation granted to him by the commander in chief”.

The US military said it also conducted strikes against Isis south-west of Kirkuk, bringing the total number of attacks against Isis targets in Iraqi territory to 194.

The White House has been under mounting pressure in recent days to show other countries, particularly in the Arab world, are willing to take an active military role in its coalition against Isis.



Last week, the secretary of state, John Kerry, promised sceptical lawmakers in a series of briefings on Capitol Hill that he would be in a position to name the unspecified active partners before the end of the week.

But it was the upcoming UN general assembly in New York, at which Obama will chair a meeting of the security council, that the politics of having countries such as Saudi Arabia, Jordan and the United Arab Emirates will be crucial for the US.



Obama is hoping to use the special session to secure international backing for a tough resolution against Isis, including an international travel ban on foreign fighters travelling from other countries.



The strikes come months in advance of any support on the ground. With Obama ruling out US combat troops for now, there is no capable ground force in eastern Syria to capitalise on the air strikes by seizing territory back from Isis.



The US plan is to train a force of Syrian rebels for that purpose in Saudi Arabia, but the training has not begun yet. The Pentagon estimates that it will take at least eight months for the first units to be ready.



Asked on Friday by the Guardian what an air campaign in Syria could accomplish without a ground component, Kirby said: “What air strikes would enable us to do is to continue to put pressure on them, particularly the safe havens and sanctuaries that they enjoy in Syria.”



The air strikes are a long-telegraphed move by the Pentagon, albeit a reluctant one for many senior military officers and the White House. In June, after Isis overran the Iraqi city of Mosul, US defence officials speculated that an American reprisal would likely need to target the group in Syria as well as Iraq, in order to inflict lasting damage.



Obama said in a televised address on 10 September that he would expand the US war against Isis into Syria, reversing a longstanding caution against involving the US in the bloody confusion of Syria’s civil war. Political and media pressure on Obama to launch air strikes against Isis and then expand the war into Syria has been intense, despite much scepticism on Capitol Hill of Obama’s war strategy.

The escalation of the war into Syria comes without explicit congressional authorisation. Last week, Congress agreed to provide $500m requested by Obama for training Syrian rebels, but deferred a vote specifically on the war against Isis until after November’s legislative elections. Obama has asserted that the 2001 Authorisation to Use Military Force against al-Qaida provides him with sufficient legal authority, something few legal scholars have embraced, owing to al-Qaida’s public rejection of Isis earlier this year.

The US has denied speculation that it will work with the government of Bashar al-Assad against Isis, a common enemy. Syria’s use of chemical weapons in its protracted civil war had earlier led Obama to consider strikes against the Assad regime. Now, the US finds itself in the position of conducting an operation that could potentially deliver strategic benefits to Assad.

General Martin Dempsey, the chairman of the US joint chiefs of staff, has warned that Assad’s air defences – mostly configured on Syria’s western coast, far from land held by Isis – are formidable, yet there is no indication that US and allied planes were under attack from Assad in the latest operation.

