The Friends of Syria alliance called on Iran and its Lebanese Hezbollah ally tonight to withdraw fighters immediately from Syrian territory.
It described their armed presence in the country as a threat to regional stability.
In a communique issued after a meeting in Amman, the alliance said any transitional government in Syria being proposed as a core of a US and Russian peace initiative must have authority over the army and the executive, which are now in President Bashar Assad's hands.
The meeting of 11 Western and Arab nations, as well as Turkey, which constitute the core group of the alliance, also warned of "severe consequences" if use of chemical weapons by Mr Assad's forces is confirmed.
Meanwhile, the World Bank has proposed a $150m loan for Jordan to help with the cost of thousands of Syrian refugees fleeing the civil war in Syria.
Close to 500,000 Syrian refugees, out of a total of 1.5m, have sought shelter in Jordan from an escalating civil war between forces loyal to President Bashar al-Assad and rebel fighters trying to overthrow him.
The cost of accommodating the refugees has further squeezed Jordan's economy, which was hit by a financial crisis last year.