The Belarusian police said on Wednesday that the personal data of 300 of its officers had been leaked online since the opposition began trying to expose the identities of members of the security forces involved in cracking down on mass protests.

Unrest since an Aug. 9 election marred by vote-rigging allegations has tested the loyalty of the security forces and their backing has become critical to president Alexander Lukashenko’s chances of clinging onto power.

During regular protests by tens of thousands of people over more than five weeks, some protesters have tried to physically unmask members of the security forces on the streets.

On Wednesday, Andrei Parshin, a senior security official at the interior ministry, said 43 criminal cases had been opened against people who he said had threatened police, the Belta state news agency reported.

“The data of about 300 police officers for the period from Aug. 9th have ended up online. More than 250 officers and their family members were subjected to pressure,” he was quoted as saying.

Lukashenko denies rigging his landslide victory in last month’s election. Many prominent opposition figures have since either been jailed or fled. (Reporting by Tom Balmforth and Maria Kiselyova Editing by Mark Trevelyan and Peter Graff)