Labour MP Diane Abbott has told Daybreak pursuit of military action against the Assad regime "runs the risk of dragging" Britain into a civil war in Syria "with no end game".
Discussing her opposition to intervention with Matt Barbet, she said: "The British public have seen this movie and they know how it ends".
The shadow health minister, though, refused to confirm reports she could resign her post if Labour leader Ed Miliband supports intervention.
Ms Abbott had earlier told the Guardian the use of military action "would put me in a very difficult position."
The Prime Minister has said 'the world should not stand idly by' after hundreds were killed in apparent chemical attacks in Syria last week.
Any UK military action in Syria would involve submarine-launched cruise missiles rather than air strikes, a military expert has predicted.