Concerns persist that rebels aim to seize the city which would aid establishing a land corridor between mainland Russia and the Russia-annexed Crimea peninsula.
The announcement -- which confirmed a Twitter posting by the rebels -- came as representatives of Ukraine, Russia, the rebels and the Organization for Security and Cooperation in Europe met in Belarus
On Saturday, rebel leader Aleksandr Zakharchenko called for a cease-fire, in a move that could be aimed at increasing international pressure on Ukraine to allow in a Russian aid mission.