KIEV (AFP) - Ukraine's Prime Minister Arseniy Yatsenyuk called on Sunday for foreign observers from the Organisation for Security and Cooperation in Europe (OSCE) to be sent "urgently" to the east and south of the country as Crimea threatened to secede and join Russia.

In a statement, the Kiev government said it had "asked that the OSCE urgently send a monitoring mission to Ukraine."

"Their mandate should include the east and south of Ukraine, including Crimea,"

Mr Yatsenyuk added in the statement, as the Black Sea peninsula voted in a referendum widely expected to favour its split from Ukraine and attachment to Russia.

"I hope this decision can be voted at an extraordinary session of the OSCE," Mr Yatsenyuk added.

More than 50 observers from the Vienna-based OSCE already attempted to enter Crimea two weeks ago in a bid to defuse tensions in the autonomous region, but were barred entry on repeated occasion at border checkpoints.

Tensions that began in Ukraine's southern region of Crimea, where Russian forces have taken de facto control, have spread in recent days to the east of the country, with pro-Moscow groups there calling for their own referendum and reattachment to Russia.