British Foreign Secretary William Hague says Iran and the militant Shi'ite group Hizballah are giving Syrian President Bashar al-Assad increasing support.
Hague, speaking at a news conference in Jordan's capital, Amman, said Assad's regime "is being propped up by others outside."
He added that Britain would urge international powers to set a date in the next few days for an international conference to try to end the two-year conflict engulfing Syria.
Hague is in Amman for a meeting of the Friends of Syria group of countries which support the anti-Assad opposition.
Besides Hague, top diplomats from Egypt, France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates, and the United States are attending the meeting.
Based on reporting by AFP and Reuters