Air strikes against the militant Khorasan Group in Syria were prompted by plans for an "imminent" terror attack on US soil, the Pentagon said.

"We believe the individuals plotting and planning it were eliminated" in the eight US air strikes, Rear Admiral John Kirby, the Pentagon spokesman, said in an interview with ABC's Good Morning America program.

US President Barack Obama delivers a statement at the White House in Washington on the air strikes in Syria. Credit:Reuters

The militant organisation was made up of a "network of seasoned al-Qaeda veterans" preparing to attack US and western interests, the Pentagon said. No further details were given about the plots.

"Last night we also took strikes to disrupt plotting against the United States and our allies by seasoned al-Qaeda operatives in Syria who are known as the Khorasan Group," President Barrack Obama said on Tuesday (local time) when addressing the air strikes in Syria. "Once again it must be clear to anyone who would plot against America and try to do Americans harm that we will not tolerate safehavens for terrorists who threaten our people."