An incident which claimed the life of an Afghan migrant near Bulgaria's border with Turkey on Thursday evening is already leaving politicians in Bulgaria divided over what actually had happened.

Police suggested hours after the development that a bullet, fired in the air as a warning of border police to a group of 54 migrants spotted near the town of Sredets, had rebounded and incidentally hit a 25-year-old man in the back of the neck.

Tsvetan Tsvetanov, a former Interior Minister and Deputy Chair of the main ruling GERB party, called for patience until the investigation establishes whether there was "aggression" committed by police and if migrants refused to heed officers' calls to stop when asked to do so, as initial reports suggest.

But MP Atanas Atahasov, a reserve general from the Reformist Bloc (RB), a member of the ruling coalition in Bulgaria, has voiced skepticism over that version.

Atanasov, who chairs the Parliament's domestic security committee, told the Bulgarian National Radio the explanation of a "ricochet in the air" was "completely not serious."

"Where did they shoot in the air so that a ricochet is produced?" he asked.

He urged that all the information available about the incident should be made public.

Valeri Simeonov, the co-chair of nationalist Patriotic Front coalition which backs the government, praised the actions of police saying anyone crossing illegally into the country should be targeted, the Bulgarian border being "sacred" in his words.

Bulgaria's Prime Minister Boyko Borisov, who left a EU summit in Brussels early to return to the country after being informed about the incident, has not yet commented.