A US official said Qatar played a supporting role in the air strikes, in what is an unprecedented and unexpected show of regional solidarity against the Isis group, which has rampaged through Syria and Iraq.
"US military and partner nation forces have begun striking Isis targets in Syria using a mix of fighters, bombers and Tomahawk missiles," said Pentagon press secretary Admiral John Kirby.
The first wave of strikes finished after about 90 minutes, but the operation was expected to continue for several more hours. Last night the Pentagon said 14 strikes were launched, including 47 cruise missiles, the BBC said.
The strikes were carried out by manned Air Force and Navy aircraft, and the Tomahawk missiles were launched from US ships in the northern Gulf and the Red Sea. The missiles were launched from USS Arleigh Burke and USS Philippine Sea.
Military officials have said the US would target militants' command and control centres, re-supply facilities, training camps and other important logistical sites.
Syrian activists reported several air strikes on militant targets in Raqqa. One Raqqa-based activist said the air strikes lit the night sky over the city, and reported a power cut that lasted for two hours. An anti-militant media collective called "Raqqa is being silently slaughtered" said that among the targets were Isis buildings used as the group's headquarters, and Brigade 93, a Syrian army base that the militants recently seized. Other air strikes targeted the town of Tabqa and Tel Abyad in Raqqa province.
France has joined the US strikes in Iraq, and the New York Times reported that "several Arab allies" had participated in the strikes against targets that included "weapons supplies, depots, barracks and buildings the militants use for command and control".
Also last night, Israel shot down a Syrian fighter jet using the Patriot air defense system after the MiG entered the country's airspace over the Golan Heights.
The US has sought global and regional legitimacy for its mission to "degrade and destroy" the Isis movement, which is responsible for atrocities including public decapitations, crucifixions and the mass execution of prisoners.
The assault came as Obama travelled to New York to attend the UN General Assembly where he will chair a meeting calling for an international agreement to curb foreign fighters from joining jihadist militants in Iraq and Syria.
The decision to conduct the air strikes was made yesterday by the head of US Central Command, General Lloyd Austin, "under authorisation granted him by the commander in chief", Kirby said.
Syria's Foreign Ministry said the United States had told it in advance about the air strikes.
Coming on the eve of the UN General Assembly in New York, the strikes carried an element of surprise. US officials had previously indicated that a sustained assault on Isis would come only once sufficient numbers of moderate Syrian rebel fighters had been trained to hold ground taken by American air power.
Until now, American and French strikes have been confined to Iraq and limited to hitting a small number of specific targets.
Officials said that the attack on Raqqa was a shift towards a sustained bombardment designed to degrade Isis capabilities in the area.
Raqqa has become the informal capital of Isis' self-proclaimed caliphate and is in the region where several foreign hostages, including two US journalists and British aid worker David Haines, were held before they were beheaded in gruesome circumstances this month.
US generals have said about two-thirds of the estimated 31,000-strong Isis fighting force is in Syria where the US has been flying intelligence gathering missions for some weeks now, building up a growing target list.
"We will be prepared to strike [Isis] targets in Syria that degrade its capabilities," Joint Chiefs of Staff chairman General Martin Dempsey told a US senate hearing last week, adding the attacks would be "persistent and sustainable".
US Defence Secretary Chuck Hagel had said that the plan included targeted actions against Isis safe havens in Syria, including its "command and control logistics capabilities and infrastructure".
US F-22 fighter jets, America's most sophisticated warplane, took part in the raids - the first combat mission for the costly aircraft - according to the Wall Street Journal and ABC News.
At a conference on September 11 with Kerry, key Arab allies promised to "do their share" to fight Isis.
The Obama Administration, which at a Nato meeting in Wales this month also got commitments from European allies as well as Canada and Australia, has insisted that the fight against Isis cannot be America's alone.
The head of the main Western-backed Syrian opposition group, Hadi Bahra, welcomed the air strikes.
"Tonight, the international community has joined our fight against Isis in Syria," he said.
"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."
How the US has justified overseas military action
Afghanistan: In the days after the September 11, 2001 terror attacks, Congress passed an Authorisation for the Use of Military Force that was meant to give President George W. Bush the ability to go after al-Qaeda in Afghanistan.
Pakistan, Yemen and Somalia: The Bush and Obama administrations have both used the force authorisation to justify drone strikes against terror targets in Pakistan, Yemen and Somalia. The US also has back-channel consent for the strikes from Pakistan's Government and a more overt agreement with Yemen.
Iraq and Syria: Congress passed an authorisation in 2002 for force in Iraq. President Barack Obama is taking action in Syria, acting under the same authorisation. Obama has called for the authorisation to be repealed but he has also used it. The White House says Obama had the power to authorise the airstrikes under way in Iraq through the commander-in-chief powers outlined in the US Constitution and it has made a similar argument regarding the airstrikes in Syria. Officials note that Iraq's Government requested US military assistance to combat Isis militants. Britain and France are not involved in the action in Syria but Paris has already conducted strikes in Iraq and London is expected to follow suit.
Libya: Obama did not seek congressional approval when the US joined Nato allies in a 2011 bombing campaign in Libya. Officials argued that the nature of the mission did not require it.
- AP
