WARSAW, Dec 29 (Reuters) - Polish prosecutors said on Wednesday they would not investigate an allegation that the phone of a high-profile government critic was hacked, amid accusations that opposition figures have been subject to illegal surveillance. Reports that sophisticated spyware developed by the Israel-based NSO Group had been used against government opponents including prosecutor Ewa Wrzosek have led to accusations that special services are undermining democratic norms. Wrzosek, a member of the group Lex Super Omnia which campaigns against what it says is the politicisation of the public prosecution service under the Law and Justice (PiS) party, received a notification in November from Apple that her phone could have been hacked using NSO Group"s Pegasus software. This month, the Associated Press reported that the Citizen Lab project at the University of Toronto found Wrzosek was one of three Polish government critics whose phones had been hacked. "The only indication that a cyberattack could have occurred ... was a message from the telephone"s manufacturer," Aleksandra Skrzyniarz, spokeswoman for the District Prosecutor"s Office in Warsaw, said in a statement explaining the refusal to investigate the case. "However, the message did not categorically state that a cyberattack had occurred, but contained a disclaimer that the alert might be false," Skrzyniarz said, adding that Wrzosek had refused to hand over the phone for examination. Wrzosek told private broadcaster TVN24 that she would appeal against the decision. "I do not see the slightest legal prerequisite or justification for the decision to refuse to initiate this procedure," she said. Polish security services do not comment on the methods they use or whether they have investigated particular people. However, spokesman Stanislaw Zaryn has denied any suggestion that Polish services were engaged in domestic political battles. Prime Minister Mateusz Morawiecki has dismissed suggestions that spyware was used by Polish services against opposition figures as "fake news". NSO says it makes technology for use by governments and law enforcement agencies to combat crime and terrorism, and has safeguards to prevent misuse. Digital rights researchers say Pegasus has been used to spy on civil society in several countries.