AMMAN: US Secretary of State John Kerry said on Sunday he and his Russian counterpart Sergei Lavrov have reached a provisional agreement on terms of a cessation of hostilities in Syria, indicating there are still unresolved issues.

"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.

Kerry said he had spoken to Lavrov earlier on Sunday and they hoped that US President Barack Obama and Russian President Vladimir Putin would be speaking in the coming days in order to complete the provisional agreement in principle, and that the two sides are "still filling out the details".