Pro-Russian protesters stormed the prosecutor's office in the separatist-held city of Donetsk on Thursday, lobbing petrol bombs and stones, Interfax-Ukraine news agency reported.

The violence broke out when protesters gathered outside the office accusing the prosecutors of working for the pro-Western government in Kiev, which Donetsk is threatening to break from in a referendum on May 11.

Protesters entered the building, and television pictures showed police filing out.