WARSAW (BLOOMBERG) - Poland's government is facing mounting pressure over its refusal to investigate allegations into the spyware hacking of political opponents.

The government's reluctance to probe the charges is a matter of concern and requires more answers, according to Citizen Lab, the cybersecurity watchdog that helped unveil the use of the controversial Pegasus spyware against a top opposition lawmaker and two others.

Donald Tusk, the former European Council president and Poland's opposition leader, called the charges the biggest "crisis for democracy" since the country overthrew communism in 1989 and called for a probe.

Prime Minister Mateusz Morawiecki has dismissed allegations that the government was responsible for spying as "fake news" and suggested it was the work of foreign intelligence agencies.

The ruling Law & Justice party has rejected calls for a parliamentary inquiry.

"I'm looking at the public statements around our investigations with puzzled wonderment," John Scott-Railton, senior researcher at Citizen Lab, said in an interview. "There's a pretty clear set of things that one should do if one thinks that this is a foreign intelligence service - and then it doesn't seem like those things are happening."

'Very concerning'

The spyware, which can track movements and communications through a user's mobile phone, has triggered outrage worldwide among rights groups as governments have been accused of deploying it against dissidents, journalists and activists.

Such activity in a European Union member state is "really startling and very concerning," Scott-Railton said.

In Poland, whose nationalist government has come under scrutiny by western allies over the erosion of judicial and media independence, the scandal is building as the ruling party struggles to secure its majority in parliament and continues its running conflict with the European Commission over the rule of law.

The government reasserted that its clandestine activities, which are classified, are carried out within the scope of Polish law and by court order.

"Operational control is carried out on persons for whom there is a justification to conduct such activities," the government said in a statement Monday in response to a query by Bloomberg News.

Citizen Lab has previously detailed the use of NSO Group Ltd's Pegasus for spying operations against dissidents.

Israel's NSO, which is struggling to survive the spyware scandal, was placed on an export blacklist by the US Commerce Department last year for activity "contrary to the national security or foreign policy interests" of the US.

Similar accusations have been raised in neighboring Hungary, where it may pose a threat to Prime Minister Viktor Orban's reelection bid this year.