"We have triggered a plan for the start of the step-by-step deployment of up to 1,000 troops along the whole Bulgarian-Turkish border (within the next week)," interior ministry chief of staff Georgy Kostov said.
It followed increased migrant pressure at the border overnight when 660 migrants attempted to cross into Bulgaria illegally, Kostov said.
The trespassers were spotted by the Bulgarian patrols, which alerted the Turkish authorities who turned them back to Turkey, he added.
EU member Bulgaria has already sent more than 1,000 extra police to its porous 260-kilometre (160-mile) Turkish border and sealed part of it with a 30-kilometre razor-wire fence that is being extended.
