Serbian authorities have warned Bulgaria it should step up border controls to stem the flow of migrants trying to cross its western border, BGNES newswire quotes Serbian police as saying.

A Serbian police official on Saturday visited the Gradina (Serbia) - Kalotina (Bulgaria) border crossing point and met with Bulgarian border authorities, asserting that as of February 22, Monday, Serbia will only deem the so-called "Western Balkans route" (Greece-Macedonia-Serbia-Croatia-Slovenia, then Austria and Germany), under an agreement reached earlier this week.

All migrants crossing into Serbia from Bulgaria will be sent back, the official explained.

He added that Sofia should work to make sure a new route is not formed via Bulgaria, especially in light of the new selection procedure that is to be introduced at the Macedonia-Greece border and the possibility that this might push migrants to seek alternative options to cross into Serbia.

Austria, Croatia, Macedonia, Serbia and Slovenia agreed in Zagreb on Thursday to introduce unified registration procedures for migrants who enter Macedonia from Greece, including biometric data of arrivals from Syria, Iraq, and Afghanistan.