(Adds new justice minister quote, measures)

By Renee Maltezou

ATHENS, Feb 23 (Reuters) - The escape of Greece's most notorious prisoner by helicopter for the second time in three years has dealt a new blow to the conservative government, still reeling from riots and a ratings slump.

The government, which has seen its popularity decline amid the world financial crisis, sacked three justice ministry officials and arrested three guards over the spectacular escape but drew scornful comments from the media and opposition parties.

The main opposition demanded the justice minister's resignation after Vassilis Palaiokostas, 44, and his Albanian accomplice Alket Rijai staged the getaway.

"In any other country ministers would have resigned," said socialist opposition PASOK spokesman, Dinos Rovlias.

"There is no public security, there is no government in Greece."

Athens dailies carried front-page headlines criticising the government for taking no measures to avoid the new embarrassment to Greek authorities, already under pressure over the police shooting of a teenager that led to the worst riots in decades in December.

"Carbon-copy fiasco, Embarrassment" said the conservative daily Eleftheros Typos. The pro-government Apogevmatini addressed a letter to Prime Minister Costas Karamanlis asking him to "put an end to the chaos".

Palaiokostas, 44, was serving a sentence for robbery and kidnapping when he first escaped with Rijai in 2006 in a helicopter. He was arrested again in August and accused of organising the kidnap of an industrialist.

He was due in court to face charges over the first escape on Monday. But on Sunday, a helicopter approached the roof of Greece's maximum security prison, threw down a rope ladder and whisked the two convicts away as prison guards watched.

Police arrested and are investigating three prison guards, a police official said.

Police found the pilot in the helicopter in a northern Athens suburb but there was no trace of the fugitives. He said he was hijacked by three people who had hired the helicopter.

A public prosecutor has asked for an investigation into prison employees' bank accounts.

"The government believes the operation wouldn't have been successful without participation from the inside. The government decided to take measures," Justice Minister Nikos Dendias said after an emergency cabinet meeting to discuss the escape.

He announced measures to improve prison security, including better recruitment and training of guards, checks on their income and enforcing a ban on mobile phones in jails. (Editing by Dina Kyriakidou and Angus MacSwan)

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