The children, aged from one to 14 years old, were killed in a shooting that police are describing as a "domestic disturbance".

Gao Zhen is being retroactively punished for 15 year-old-works, in a case that has alarmed rights groups.

Exit polls put his Progressive Bulgaria on 37%, more than double the score of the closest runner-up, but he will likely need to form a coalition to govern.

Tehran has not commented on the incident, which comes as the US prepares for a second round of talks.