US Secretary of State John Kerry says he and his Russian counterpart Sergei Lavrov have reached a provisional agreement on terms of a cessation of hostilities in Syria, with the sides closer to a ceasefire than ever before.
But he indicated on Sunday there were still issues to be resolved and he did not expect any immediate change on the ground.
It comes as twin car bombs claimed by Islamic State killed at least 57 people in Homs on Sunday, and bombings killed at least 30 in a suburb of Damascus.
Russian air strikes launched in September against rebels fighting President Bashar al-Assad have exacerbated suffering and destruction in Syria, where a five-year-old civil war has killed more than a quarter of a million people.
Assad said on Saturday he was ready for a ceasefire on condition "terrorists" did not use a lull in fighting to their advantage and that countries backing insurgents stopped supporting them.
The Syrian opposition had earlier said it had agreed to the "possibility" of a temporary truce, provided there were guarantees Damascus's allies including Russia would cease fire, sieges were lifted and aid deliveries were allowed country-wide.
"We have reached a provisional agreement in principle on the terms of a cessation of hostilities that could begin in the coming days," Kerry told a news conference in Amman with Jordanian Foreign Minister Nasser Judeh on Sunday.
"The modalities for a cessation of hostilities are now being completed. In fact, we are closer to a ceasefire today than we have been," said Kerry, who was also to meet King Abdullah.
But he repeated the US position that Assad had to step down.
Assad's fate has been one of the main points of difference between Washington and Russia, the Syrian leader's main international backer. Russia recently has begun to say Syrians should decide on whether Assad should stay or not, but it continues to support Damascus with air strikes.
Kerry said he had spoken to Lavrov on several occasions, including earlier on Sunday, and that he anticipated US President Barack Obama and Russian President Vladimir Putin would talk in the coming days to complete the provisional agreement in principle.
