William Hague is to meet Syrian opposition leaders fighting to oust president Bashar Assad's brutal regime.
The Foreign Secretary will urge the group to develop a clear plan for political transition in Syria when he opens the London talks, which are being hosted by the UK's special envoy, Jon Wilks.
He will also press for the need to respect human rights and "win over the middle ground of opinion" in the nation amid the spiralling violence meted out by the regime.
Mr Hague said work with the opposition coalition, which was formed at the weekend in an effort to unite disparate factions in the fight against Assad, was a "high priority".
The US and the UK have signalled support for the group but stopped short of the formal recognition of it as a government-in-waiting already accorded by France.
It comes after Prime Minister David Cameron chaired National Security Council (NSC) discussions between ministers and officials on Thursday on military, humanitarian and diplomatic options for halting the violence and refugee crisis.
He last week ordered all options, including arming rebel forces opposed to Assad, to be put back on the table amid frustration at international failure to curb the bloodshed.
Among controversial strategies being considered by Mr Cameron is allowing Assad a safe passage out of Syria even if that means he evades international justice.
Downing Street said the hour-long NSC meeting involved "a thorough discussion of the full range of options" - military as well as political and diplomatic.
Officials are also examining the terms of the EU embargo which prevents the UK directly supplying the rebels with arms for ways to justify such a move. The Prime Minister said last week, after visiting a refugee camp in Jordan, that he would make the crisis a top priority in working with the US during Barack Obama's second term.