Syrian opposition leaders will meet Foreign Secretary William Hague to discuss what role the UK could play in bringing about a political solution to the conflict in Syria.
Monzer Akbik of the Syrian National Coalition (SNC) said other countries would form a "coalition of the willing" to launch strikes against Assad even without the UK's involvement.
He told BBC2's Newsnight that the international community had a duty to "take measures in order to paralyse the ability of the war machine of the regime to kill".
More top news
How is Sainsbury's positioned to tackle the challenges of low-cost rivals and changing shopping habits?
The head of football's anti-discrimination body Kick It Out has responded to attacks by QPR defender Rio Ferdinand in his autobiography
Prime Minister David Cameron and his wife Samantha surprised diners in Solihull by dropping into fast food chain Five Guys for burgers.