Jordanian mediation has brought Syrian rebel negotiators back to the table with Russian officers to discuss a final deal to end fighting and restore Syrian state control of Deraa province, a Syrian opposition spokesman said.
Ibrahim al Jabawi said the two sides were expected to hold talks this evening in the southern town of Busra al Sham. Four rounds of talks have been held there since Saturday, without reaching agreement.
Rebel officials say the main differences include whether the rebels surrender their weapons in one go or in phases, before handing over their areas to state control under Russian military police supervision.
Jordan has played a leading role behind the scenes in persuading Free Syrian Army rebels, whom it and Western powers have long supported, to reach a deal with Russia that could spare southern Syria more bloodshed and destruction.
Tens of thousands of Syrians have fled the fighting in the region towards Jordan's border.
Jordanian Foreign Minister Ayman Safadi held talks on Wednesday in Moscow, where he warned a humanitarian crisis threatened to unfold on the border and said a ceasefire was urgently needed.
On Thursday, Russian planes hit areas close to the Jordanian border. A major battle was raging in an air base on the outskirts of Deraa city, only a few kilometres (miles) from Jordan's northern city of Ramtha, residents and diplomats said.