BENGHAZI, Libya — A strong explosion ripped through the main police building in the eastern Libyan city of Benghazi early on Friday, nearly flattening it, days after Islamic militias overran army barracks and claimed control of the city.
The police headquarters has been empty for several days after militias pounded it with shelling.
Friday’s blast appeared to be from explosives planted inside the building, said witnesses at the site. They spoke on condition of anonymity, fearing for their safety.
Also Friday, Tunisia closed its main border crossing with Libya after thousands of stranded Egyptian and foreign nationals, fleeing the violence in Libya, tried to break through the passage, the Tunisian news agency said. It was the second eruption of unrest at the border in as many days. Tunisia is the only escape route as fighting escalates in the Libyan capital, Tripoli
A coalition of Islamic militias over the past week captured a number of army bases in Benghazi, driving out troops and police and seizing large weapons stores. The fighting takes place at a time that rival militias in Tripoli have been battling for weeks over control of its airport.
The spiral of violence in the country’s two main cities could be sparking a popular backlash, with calls for large rallies on Friday to protest against militias and demand the return of the police and military.
‘‘It’s time for a popular uprising to rescue Libya,’’ said Abdel-Moneim al-Yassir, a lawmaker in the outgoing Parliament and head of its National Security Committee.