Greece's Prime Minister claimed on Monday that accusations that he wiretapped his own ministers were "an incredible lie," as the main opposition party proposed a no-confidence vote in the wake of the scandal.

Kyriakos Mitsotakis' conservative government came under heightened scrutiny after a bombshell media story over the weekend claimed that state monitoring had targeted more than 30 lawmakers, journalists, and business executives.

The Supreme Court has ordered an investigation and the far-left party of former Prime Minister Alexis Tsipras, Syriza, demanded the government to shed light on the affair before the next election due in 2023.

On Monday, Mitsotakis was not happy, calling the report by the left-wing weekly newspaper Documento, linked to Syriza, "shameful".

"We have a publication revealing a series of people allegedly under surveillance without the faintest proof that that was actually happening," he told private channel Antena1.

"I have never claimed there wasn't any surveillance. It's another thing to accuse the prime minister of orchestrating this action," he added, calling the accusations "shameful" and "unacceptable".

Documento claimed on Saturday that the mobile phones of 33 high-profile public figures had been illegally targeted by Predator malware and technologies used by the government intelligence agency EYP.

Former Prime Minister Antonis Samaras, many senior cabinet ministers, and shipping mogul Vangelis Marinakis, owner of Olympiakos and Nottingham Forest football teams, are among the alleged targets.

Influential members of Mitsotakis' conservative New Democracy party, who could be opponents in any future leadership race, are also said to have been wiretapped.

'All options on the table' 

Syriza said it was considering tabling a motion of no-confidence. "All options are now on the table. We will use them at an opportune moment," Syriza said.

The government spokesperson, which has a comfortable majority in parliament, said there were "no elements of proof" to support Documento's revelations.

The scandal broke in July when Nikos Androulakis, an MEP and leader of the Socialist party (PASOK), complained over alleged attempts to tap his mobile phone using Predator spyware.

Within days, it was revealed that Androulakis had been under separate observation by the national espionage agency before becoming leader of PASOK, the country's third-largest party. Two journalists and another senior opposition politician also claim to have been spied on.

The scandal forced the resignations in August of the intelligence agency boss and of a close aide and nephew to the Prime Minister.

The government has categorically rejected the use of illegal spying software. It has, however, admitted that the state intelligence service tracked Androulakis, without explaining why.

Mitsotakis has pledged to bring in a law banning the sale of malevolent spyware. Critics point out, however, that one of his first moves as Prime Minister in 2019 was to link the national intelligence service to his personal office.

A European Parliament committee looking into wiretaps in Greece and other European Union countries asked for a more thorough inquiry on Friday. Its preliminary report is due on Tuesday.