Two Bulgarian police officers were killed as they tried to stop a bus containing migrants who had entered the country illegally, a senior interior ministry official said.

The incident occurred at 5am local time in the Black Sea city of Burgas after the bus refused to stop at two consecutive border police checkpoints, Stanimir Stanev told reporters.

The bus, with Turkish registration plates, was carrying 47 migrants whose nationality has not been disclosed.

The bus had entered a residential area when the police officers halted their car across the road in front of it. The bus rammed the police vehicle, then drove over the top of it before smashing into a bus stop.

The two officers in the car were killed instantly. No other injuries were reported and an investigation into the case has been launched.

So far, no charges against the driver have been brought, but district prosecutor Georgi Chinev called the driver’s actions a “conscious, purposeful act”.

Bulgaria, a Balkan country of seven million people, is located on a major route for migrants from the Middle East and Afghanistan to Europe.

Only a small number of them plan to stay in the EU’s poorest member, using Bulgaria instead as a transit corridor on their way westward.