By Phil Stewart and Tom Perry

WASHINGTON/BEIRUT (Reuters) – The United States and Arab allies bombed Syria for the first time on Tuesday, killing dozens of Islamic State fighters and members of a separate al Qaeda-linked group, pursuing a campaign against militants into a war at the heart of the Middle East.

“I can confirm that U.S. 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.

U.S. Central Command said Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates participated in or supported the strikes against Islamic State targets around the eastern cities of Raqqa, Deir al-Zor, Hasakah and Albu Kamal.

Targets included “fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance center, supply trucks and armed vehicles,” it said.

EXTRA: Allies join U.S. in fight against ISIS

Separately, U.S. forces acting alone launched strikes in another area of Syria against an al Qaeda-linked group, the Nusra Front, to “disrupt imminent attack” against U.S. and Western interests by “seasoned al Qaeda veterans”, CentCom said.

The Syrian Observatory for Human Rights, which monitors the war in Syria, said at least 20 Islamic State fighters were killed in strikes that hit at least 50 targets in Raqqa and Deir al-Zor provinces in Syria’s east.

It said strikes targeting the Nusra Front in the northern provinces of Aleppo and Idlib had killed at least 50 fighters and eight civilians. The Nusra Front is al Qaeda’s official Syrian wing and Islamic State’s rival. The Observatory said most of the fighters killed there were not Syrians.

Islamic State vowed revenge.

“These attacks will be answered,” an Islamic State fighter told Reuters by Skype from Syria, blaming the “sons of Saloul” – a derogatory term for Saudi Arabia’s ruling family – for allowing the strikes to take place.

The strikes took place hours before Obama goes to the U.N. General Assembly in New York where he will try to rally more nations behind his drive to destroy Islamic State.

SYRIAN GOVERNMENT INFORMED

The Syrian government said Washington had informed it hours before the strikes. Secretary of State John Kerry had sent a letter to Damascus through his Iraqi counterpart, it said.

(Additional reporting by Alexander Dziadosz and Mariam Karouny in Beirut, Lesley Wroughton, Steve Holland and Matt Spetalnick in Washington; Writing by Peter Graff; Editing by Paul Taylor)