(Updates with socialist leader's reaction)
By George Georgiopoulos and Renee Maltezou
ATHENS, Aug 8 (Reuters) - Greek Prime Minister Kyriakos Mitsotakis reiterated on Monday that he was unaware that Socialist Party (PASOK) leader Nikos Androulakis' phone had been tapped in 2021, seeking to distance himself from a growing political scandal.
The case, which broke last week, has sparked uproar, with opposition parties demanding a thorough investigation and labelling the revelations Mitsotakis' personal Watergate.
The prime minister, whose party faces an election next year, apologised to Androulakis on Saturday, saying that he had no knowledge of the intelligence service tap and that he would not have approved it.
On Monday Mitsotakis added in a speech to the nation: "What took place may have been lawful but it was a mistake. I did not know and obviously I would have never allowed it."
He said he had only found out about Androulakis' wiretapping "a few days ago", and also announced measures to tighten control of the EYP intelligence service's operations and boost transparency over its practices.
He said the EYP intelligence service had underestimated the political dimension of its surveillance which, while complying with the law, was "politically unacceptable."
Androulakis, a member of European Parliament since 2014 who was elected PASOK party leader in December 2021, said on Friday he had learned EYP listened to his conversations in late 2021.
Reacting to what he called Mitsotakis' "narrative of a lawful mistake", Androulakis said the prime minister had tried to buy time with Monday's TV address but that he would soon have to face the truth.
"I will not accept any cover up, the clock is ticking against him," Androulakis said in a statement, adding that Mitsotakis had tried to downgrade a case that bears on the separation of powers in Greece.
PASOK is Greece's third-largest political party and was for decades the main political rival of Mitsotakis's conservative party, New Democracy.
Last week EYP head Panagiotis Kontoleon and the prime minister's chief of staff Grigoris Dimitriadis unexpectedly resigned over the case.
The main political opposition, the leftist Syriza party, said Mitsotakis had failed to answer burning questions, including why Androulakis was deemed a national security threat and was wiretapped.
Mitsotakis said the case highlighted the need for additional safety filters in intelligence operations, proposing to boost the oversight of the spy service by the parliament's committee on institutions and transparency. (Reporting by George Georgiopoulos and Renee Maltezou; editing by John Stonestreet and Hugh Lawson)