U.S. Secretary of State John Kerry reportedly said Sunday he had reached a provisional agreement on terms of a cessation of hostilities in Syria with his Russian counterpart Sergei Lavrov. Kerry made the announcement at a news conference in Amman with Jordanian Foreign Minister Nasser Judeh.

"We have reached a provisional agreement in principle on the terms of a cessation of hostilities that could begin in the coming days," Kerry said, adding that he had had repeated conversations with Lavrov, including the one on Sunday to arrive at a temporary truce in Syria.

Kerry, however, did not reveal any details of the deal and said he didn't expect fighting to cease immediately.

"I do not believe that in the next few days, during which time we try to bring this into effect, there is somehow going to be a tipping point with respect to what is happening on the ground. ... The opposition has made clear their determination to fight back," Kerry said, according to Reuters.

The announcement followed softening in the stance of Syrian President Bashar Assad Saturday, who said he was ready for a ceasefire on the condition that "terrorists" did not use a lull in fighting to their advantage.

The main U.S.-backed Syrian opposition group also said Saturday it was ready "in principle" to implement a temporary ceasefire in Syria if given guarantees that Assad’s allies, including Russia would stop attacks, sieges were lifted and humanitarian aid deliveries were allowed in the war-ravaged country.

The Russian Foreign Ministry also confirmed Lavrov and Kerry had spoken about conditions for a ceasefire in Syria on the telephone on Sunday, according to Reuters.

"The modalities for a cessation of hostilities are now being completed. In fact, we are closer to a ceasefire today than we have been," Kerry reportedly said, adding that the two sides are "filling out the details."

Indicating that the negotiations were yet to iron out all the differences, Kerry said that he anticipated that U.S. President Barack Obama and Russian President Vladimir Putin would be speaking in the coming days in order to complete the provisional agreement in principle.

On Friday, Russia had asked for any plans of a ground invasion into Syria to be scrapped, in a draft resolution to the U.N. council. While Turkey and Saudi Arabia have said they could commit ground forces earlier in February, both nations have backtracked on their remarks since then.