EU Parliament President Martin Schulz warned Bulgarian authorities must protect the EU's external borders regardless of the fact that the country is not part of the Schengen borderless area.

Schulz made his comment on Thursday evening after attending an EU summit where the migrant crisis was the first item on the agenda.

"In my view, the efficient protection of the Bulgarian-Turkish border is of mutual interest. Frankly, this obligation has nothing to do with whether you are a member of Schengen or not," Schulz said when asked by the Bulgarian National Radio if the lack of access to Schengen information constituted any hindrance whatsoever to Bulgaria's efforts to protect the border.

"Protection of the [EU]'s external border, with or without Schengen, is based on the same criteria. This is why you see how controversial the decision not to admit your country was."

He is also quoted as saying the refusal has been a "political" one, despite Bulgaria and Romania having fulfilled the technical criteria.

This comes as Bulgaria insisted it should either join Schengen or use its database to provide better border protection amidst the migrant crisis.

The EU Summit on Thursday began just before a migrant crossing into Bulgaria from Turkey was shot dead by border police, with authorities claiming a bullet fired in the air had ricocheted, hitting the back of the man's neck.