British Tornado jets hit seven targets in eastern Syrian oil fields in a mission described as landing a “very real blow” by Defence Secretary Michael Fallon.
But Free Syrian Army spokesman Issam al-Reis told BBC Radio 4’s Today programme it “will not make a big difference”.
“It will be just a few more jets, (which have been) flying across Syria and hitting Isis for more than a year,” Mr al-Reis said. “The difference will be on the ground.
“Without boots on the ground it will be difficult to make any change.”
Mr Cameron is under fresh pressure over his claims that 70,000 fighters in Syria would be able to take on IS.
The Times quoted a senior Whitehall source warning that the figure could become the equivalent of Tony Blair’s “dodgy dossier” claims ahead of the Iraq War.
“There were Ministry of Defence officials who maybe felt scarred after the previous dossier,” the source said.
“They looked at the latest text and said that (the 70,000 figure) could become the ’45 minutes’ moment of this document.”
But a senior MoD source told the Press Association: “As far as I’m aware we were fine with it (the 70,000 figure).”
Downing Street also insisted that no concerns had been raised by the MoD before the Prime Minister revealed the 70,000 figure in the Commons.
A Number 10 spokeswoman said: “The 70,000 figure was produced by the Joint Intelligence Committee, which includes in its membership officials from the Ministry of Defence.
“The Ministry of Defence did not raise concerns with No 10 on whether this figure should be included in the PM’s response to the Foreign Affairs Committee.”
Germany’s parliament is due to vote today on whether to provide military support in the fight against IS.