The US President Barack Obama has said the battle against Islamic State is not "America's fight alone", speaking after the US launched airstrikes against the militant group in Syria.
Mr Obama, speaking from the White House, also said the US would continue to build a coalition to defeat the Islamist militants.
The US was joined by five Arab nations in protracted raids that used land- and sea-based US aircraft as well as Tomahawk cruise missiles launched from two Navy ships in the Red Sea and the northern Persian Gulf.
At least 70 IS fighters are said to have been killed in dozens of attacks, which also targeted al-Qaeda veterans.
The US has targeted IS facilities in Iraq but this is the first time the campaign has expanded into Syria, a country marred by three years of civil war.
The US military said it had destroyed or damaged multiple IS targets around the militant stronghold of Raqqa as well as Deir al Zor, Hasakah and the border town of Albu Kamal.
It said targets included IS fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance centre, supply trucks and armed vehicles.
The five Arab nations - Saudi Arabia, Qatar, Bahrain, Jordan and the United Arab Emirate - either participated in the airstrikes or provided unspecified support, US officials said.
Jordan said its air force had bombed "targets that belong to some terrorist groups that sought to commit terrorist acts inside Jordan".
Separately, the US alone carried out eight airstrikes to disrupt what the military described as "imminent attack plotting against the United States and Western interests" by a network of al-Qaeda veterans.
Mr Obama had been wary of dragging the US military into the conflict between the regime of President Bashar al-Assad and rebel groups.
But he said 40 countries have now offered to help confront the terrorist threat.
Damascus says the US had informed Syria's envoy to the UN about the strikes.
Activists said the airstrikes hit targets in and around the Syrian city of Raqqa and the province with the same name. Raqqa is the Islamic State group's self-declared capital in Syria.
International efforts to combat the group have taken on an added urgency after the beheading of US journalists James Foley and Steven Sotloff and British aid worker David Haines, and the threat to kill UK hostage Alan Henning.
The strikes did not involve the UK, but British Prime Minister David Cameron supported them and will discuss at the United Nations what contribution Britain can make, according to Downing Street.
Photographs taken in Raqqa showed wreckage of what IS fighters said was a drone that had been shot down. Pieces of the wreckage, including what appeared to be part of a propellor, were shown loaded into the back of a van.
Speaking earlier to the Pat Kenny Show, Robert Fisk said "if aircraft of the Arab world have actually been attacking ISIS, that is a development that could have a critical role in the future".
He also explained how the Syrian regime is likely to be responding to the air strikes.
The US Navy has released a video of the USS Arleigh Burke (DDG 51) launching Tomahawk Land-Attack Missiles (TLAM) against IS targets:
Originally posted 7:16am
