British Foreign Secretary William Hague warned Friday that the conflict in Syria threatens to tear the country apart completely unless a solution is found in 2014.
"If the conflict continues, Syria itself could disintegrate and with extremism growing create ungoverned space in the heart of the Middle East," he said at the opening of the annual Manama Dialogue on security.
Speaking in Kuwait earlier, the British foreign minister said Syrian President Bashar al-Assad must stand down to allow for any peaceful settlement to the 33-month-old conflict.
"We have always been very clear that a peaceful solution in Syria must require the departure of President Assad," Hague told reporters in Kuwait City after talks with his Kuwaiti counterpart Sheikh Sabah Khaled al-Sabah.
"It is impossible to imagine after so many deaths, so much destruction, a regime oppressing and murdering its own people on this scale" should remain in power, Hague said.
"It is impossible to imagine, I think, President Assad could remain on the scene in Syria in the future," he said.
The reiteration of Britain's call for Assad's ouster came just weeks ahead of an international peace conference on Syria slated for January 22.
The government in Damascus has said Assad will remain president and lead any transition agreed at the conference, while the opposition and rebels fighting the regime insist he play no role.
Hague said Assad remaining at the helm was "an obstacle to peace," and that he would not be accepted by Britain or any other Western country.
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But no Western power could guarantee when Assad departs.
"We believe it is imperative for him to go," said Hague, renewing Britain's recognition of the opposition Syrian National Coalition as the legitimate representative of Syria's people.
Coalition chief Ahmad Jarba is due in Kuwait early Saturday on his first official visit to the Gulf state.
The Kuwaiti foreign minister stressed the importance of the visit, ahead of both the Geneva 2 peace conference and a "Kuwait 2" donor conference in Kuwait City set for mid-January.
In his speech to open the Manama Dialogue, which US Defence Secretary Chuck Hagel is due to address on Saturday, Hague said both sides have to compromise.
"On January 22 both the regime and the opposition have to go to Geneva ready to make the necessary compromises," he said.
"Ending the syrian conflict will be an extraordinarily difficult task: it requires the parties themselves to decide they have more to gain from negotiating than from fighting.
"We have to try to make this a decisive year. If we don't we will face a humanitarian crisis of potentially unmanageable proportions," he said.
He said if current trends continue, more than four million Syrians would be refugees -- "a fifth of the population of the entire country".
Hague said it was "inconceivable that Assad and his close associates could play any role in the future of Syria".