An influential parliamentary committee has written to Foreign Secretary William Hague demanding to know whether the Government was making preparations for "imminent" UK involvement in military action in Syria.
The House of Commons Foreign Affairs Committee asked Mr Hague to confirm whether the Government has sought legal advice on the lawfulness of any such intervention, and whether MPs will be given a vote on any decision to deploy military forces.
In a letter to the Foreign Secretary, committee chairman Richard Ottaway said that the FAC was growing "increasingly concerned that momentum is building toward some form of Western-backed military action and that the Government is considering becoming involved in such action imminently, without consulting Parliament".
Mr Ottaway said there were "grave concerns" among some MPs about the "value, legitimacy and legality" of any Western intervention and warned that the circumstances in Syria were "very different" from the widely-supported international operations in Libya in 2011, which were backed by a United Nations resolution.
Speculation that the Government may be considering military action was fuelled by Mr Hague's statement to last week's Friends of Syria meeting in Morocco that "we do not rule out any option to save lives" in the Middle Eastern state, where president Bashar Assad is fighting an uprising which has lasted 21 months.
In the letter, Mr Ottaway also noted that Prime Minister David Cameron told the Commons that Britain should now "explore all options to support the opposition and to enable greater support for the protection of civilians".
The UK last month formally recognised the main Syrian opposition umbrella group, which is also regarded by the United States, France and several Gulf states as the sole legitimate representative of the Syrian people.
And at a meeting in Brussels last week, the European Council asked foreign ministers from the 27-nation bloc to "work on all options to support and help the opposition and enable greater support for the protection of civilians".
Mr Ottaway told the Foreign Secretary that the committee "share your desire for an urgent end to violence and welcome your efforts so far to encourage international unity and resolve to find a peaceful solution". The cross-party group condemns the Assad regime's repression of its own people, he said.