The European Union's border agency Frontex said on Thursday it will triple the number of its officers in Bulgaria from next month to help stem the amount of people crossing into the bloc from Turkey. The staffing boost comes as Bulgaria prepares to partially join Europe's open-travel Schengen Zone, a move which will scrap passport checks for people travelling between the country and that area by air and sea from March 31. The staffing boost would bring the number of officers working there to between 500-600, Frontex chief Hans Leijtens said, standing near the frontier's barbed wire-topped fence.