A Tomahawk cruise missile is launched from the US Navy guided-missile destroyer USS Arleigh Burke. Photos: US Navy handout via Reuters

The United States and its Arab allies bombed Syria for the first time yesterday, killing scores of Islamic State (IS) fighters and members of a separate al-Qaeda-linked group, opening a new front against militants by joining Syria’s three-year-old civil war.

In a remarkable sign of shifting Middle East alliances, the attacks encountered no objection – even signs of tacit approval – from President Bashar al-Assad’s Syrian government, which said Washington gave advance notice.

US Central Command (CENTCOM) said Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates participated in or supported the strikes against IS targets.

All are countries hostile to Assad but now fearful of the fighters that have emerged out of the anti-Assad rebellion they backed.

US President Barack Obama said in a televised statement that the breadth of the coalition, including the five Arab states, showed the United States was not alone.

The White House said some of the strikes had been conducted to disrupt an al-Qaeda affiliate known as the Khorasan Group, which it said had been plotting an imminent attack either in the US or in Europe.

“Once again, it must be clear to anyone who would plot against America and do Americans harm that we will not tolerate safe havens for terrorists who threaten our people,” Obama said before leaving the White House for the United Nations in New York, where he planned more talks to enlarge his alliance.

Warplanes and ship-launched Tomahawk cruise missiles struck dozens of targets including fighters, training compounds, headquarters and command and control facilities, storage sites, a finance centre, trucks and armed vehicles, CENTCOM said.

“I can tell you that last night’s strikes were only the beginning,” Rear Admiral John Kirby, a US Defence Department spokesman, told reporters. The overnight attacks had been “very successful”, he said, but gave few details and would not discuss casualties.

Washington also said US forces had acted alone to launch eight strikes in another area of Syria on the Khorasan Group, which US officials have described in recent days as posing a threat similar to that from IS.

The Syrian Observatory for Human Rights, which monitors the war in Syria, said at least 70 IS fighters were killed in strikes that hit at least 50 targets in the provinces of Raqqa, Deir al-Zor and Hasakah.

It said at least 50 fighters and eight civilians died in strikes targeting al-Qaeda’s Syrian affiliate, the Nusra Front, in northern Aleppo and Idlib provinces, and most were not Syrians.

We are not part of the alliance. But there is a common enemy- Syrian analyst Ali al-Ahmad

The air attacks fulfil Obama’s pledge to strike in Syria against IS, a Sunni Muslim group that has seized swathes of Syria and Iraq, slaughtering prisoners and ordering Shi’ites and non-Muslims to convert or die.

It remains to be seen how effective air strikes can be against IS in Syria, where Washington lacks a strong ally to fight the group on the ground. The militants vowed reprisals, and an allied group is threatening to kill a French hostage captured in Algeria.

In a sign of how IS’s rise has blurred conflict lines, the Syrian government said Washington had informed it hours before the strikes in a letter from Secretary of State John Kerry sent through his Iraqi counterpart.

The Pentagon said the US Ambassador to the United Nations, Samantha Power, had informed Syria’s envoy in advance but there had been no coordination nor communication between the two countries’ armed forces.

The Syrian foreign ministry refrained from criticising the action. State media reported a senior Iraqi envoy briefed Assad on the next steps and the Syrian leader said he supported any international effort to fight terrorism.

Only a year ago Washington was on the verge of bombing the Syrian government over the use of chemical weapons, before Obama cancelled the strikes at the last minute.

Tightly controlled Syrian state TV interviewed an analyst who said the air strikes did not amount to an act of aggression because the government had been notified.

“This does not mean we are part of the joint operations room, and we are not part of the alliance. But there is a common enemy,” said the analyst, Ali al-Ahmad.

Syria’s closest ally, Iran, responded cautiously. President Hassan Rouhani neither condemned nor endorsed the action but said that without a UN mandate or request from the affected state’s government, military strikes “don’t have any legal standing”.

Residents of the city of Raqqa, Islamic State’s de facto capital in eastern Syria, said by telephone that people were fleeing for the countryside after the bombs fell overnight.

IS vowed revenge against the US. “These attacks will be answered,” a fighter told Reuters by Skype from Syria, blaming Saudi Arabia’s ruling family for allowing the strikes.

The Sunni fighters, who have proclaimed a caliphate ruling over all Muslims, shook the Middle East by sweeping through northern Iraq in June. In recent weeks they killed two US journalists and a British aid worker, raising fears that they could attack Western countries.

None of Washington’s traditional Western allies has so far joined the campaign. Britain said it was still considering its options, with Prime Minister David Cameron due to set out his position in a speech to the UN General Assembly in New York today, while France has struck IS in Iraq but not in Syria.