Bulgarian police have arrested 18 migrants trying to cross into Serbia, authorities say.
Border police officers have found 15 men and 3 women moving toward Serbia, around a kilometer before the border itself.
Most of the irregular migrants are from Pakistan, Afghanistan and Iraq and have alerady been registered with the State Agency for Refugees, Focus News Agency quoted police as saying.
Three others have failed to show identity documents.
Serbia raised awareness earlier this summer of a substantial migrant inflow from Bulgaria, a claim Sofia denied.
Security was stepped up along the frontier after Belgrade voiced its concerns.
At the border with Turkey, as many as 87 have tried to enter Bulgaria since Sunday began, according to police estimates.