The Organisation for Security and Cooperation in Europe (OSCE) have agreed to send an observer mission to Ukraine.
The US mission to the OSCE said on Twitter that a consensus was reached at a meeting of the group's 57 members, who include European Union nations, Russia, Ukraine and the US.
Western countries - particularly Germany - have been pushing hard for an observer mission as a way of preventing an escalation of tensions in Ukraine's south and east, which have a large Russian-speaking population, following Russia's annexation of the Crimean Peninsula.
The mandate calls for an initial deployment of 100 civilian monitors to regions in the east, south and west. Up to 400 more could be added "as necessary and according to the situation".