King Abdullah II of Jordan received a phone call from Syrian President Bashar al-Assad, the royal palace said on Sunday in what officials said was the first such communication since the start of the conflict in Syria a decade ago. 

The conversation was the latest step in thawing relations between leaders who had long been on opposing sides in Syria's civil war, with Jordan supporting Syria's Western-backed mainstream rebels seeking to drive Assad from power. 

"They discussed relations between the two brotherly countries and ways of enhancing cooperation," the Jordanian palace statement said. 

King Abdullah told Assad his country supported the territorial integrity of its northern neighbor and efforts to preserve its "stability and sovereignty," the palace statement said. 

Jordan, the staunch U.S. ally has, however, in the last few months accelerated steps to normalize ties with Syria and nearly two weeks ago received the Syrian defense minister in a rare visit to coordinate cross-border security. 

King Abdullah said in an interview with CNN in July that Assad was there to stay and that the status quo that kept Damascus ostracized by the international community was untenable.

The U.S. State Department said on Wednesday that Washington has no plans to "normalize or upgrade" diplomatic relations with Assad's government and also does not encourage others to do so. 

Jordan is prodding Washington to lift parts of the 2019 Caesar Act – the toughest U.S. sanctions yet that prohibited foreign companies trading with Damascus that has hampered wider dealings with Syria, a senior official said. 

Amman was waiting for a U.S. waiver that will allow its state airliner Royal Jordanian (RJ) to resume direct flights to Damascus for the first time since the outset of the conflict, the official who requested anonymity said. 

Jordan last week fully reopened a border crossing with Syria to boost investment and trade that had suffered during the decade-old conflict. 

(Cover: A combination photo of Jordan's King Abdullah (L) and Syrian President Assad (R). /AFP )