ROME - Just weeks ago Silvio Berlusconi appeared to have an ironclad grip on power. Now the Italian leader is looking suddenly vulnerable, with the heat coming from something almost unheard of in freewheeling Italy: a sex scandal.

Opposition politicians and newspapers kept up the pressure Wednesday on Berlusconi, who has spent most of the past month defending himself against accusations from his wife that he had an inappropriate relationship with an 18-year-old model.

In the latest fallout from the scandal, Berlusconi has come under attack over his explanations for using a government airplane to fly friends, entertainers and starlets for parties at his vacation villa in Sardinia. The opposition charged Wednesday that Berlusconi has nearly tripled the use of government flights from the previous leftist administration.

The prime minister's office felt obliged this week to deny any misuse of a state airplane to fly friends to Sardinia after a consumer group complained. It said the added passengers did not increase costs.

But Berlusconi, who has ruled for seven of the past eight years, appears to be losing his teflon touch amid the growing public relations disaster: newspapers published photos this week of people disembarking from the government plane, identifying one young woman as a flamenco dancer and a man as a Neapolitan crooner.

The scandal is clearly getting to the usually ebullient prime minister.

As he arrived at the presidential palace this week for a national day reception, Berlusconi looked decidedly out of sorts as jeers mingled with cheers among the gawkers waiting outside.

"Scoundrel!" shouted one man as Berlusconi entered the Renaissance-era palazzo. Inside, the 72-year-old media baron just smiled wanly and mumbled "Okay" when a reporter asked how he was doing.

Italians have long winked at the peccadilloes of their political leaders, taking it almost for granted that men in power would have the occasional fling and surround themselves with beautiful women.

The uproar is all the more surprising because of Italians' tolerant attitudes to sex and their respect for the private lives of politicians.

Italians were mystified that U.S. President Bill Clinton's dalliance with a White House intern could produce such scandal, blaming it on a hypocritical American puritanism and assuring it couldn't happen here.

But a combination of factors - sympathy for a spurned wife, Berlusconi's ongoing legal problems and upcoming European Parliament elections that energized an otherwise weak opposition - has kept the saga going. The Italian news media has not shied from the story, led by the left-leaning La Repubblica, which Berlusconi's estranged wife used to attack her husband.

The prime minister felt obliged to appear on national television to reject his wife's suggestions that he had a sexual relationship with 18-year-old glamour girl Noemi Letizia, calling it a "lie" and demanding she apologize.

Berlusconi, known for his colourful quotes and frequent gaffes, in the past has confounded his critics and political opponents, winning a landslide election victory last year despite corruption charges still hanging over his head.

But the latest scandal comes as a big embarrassment and a potential political blow, coming ahead of this week's European elections and Berlusconi's hosting of U.S. President Barack Obama and other leaders of the Group of Eight leading industrial countries in July.

"Americans had been made fun of by many Italians who described them as being puritans or exaggeratedly interested in the private life of their president," said Aldo Grasso, a leading social commentator.

"But now, and always for political reasons, we are making the same mistakes."

Berlusconi's second wife, former actress Veronica Lario, has for years lived a very separate life from her billionaire husband. She announced in May that she had hired a lawyer to begin separation and divorce proceedings.

In particular, she lashed out at his reported attendance at Letizia's 18th birthday party in Naples. She said she was surprised "because he never came to the 18th of any of his children, even though he was invited."

Berlusconi has taken to television and the newspapers to deny anything untoward. "I have sworn it on the life of my children," he said last week, adding he would resign "in an instant" if there were any truth to the whispers.

Berlusconi said during a TV show on Wednesday that he had promised to go to Letizia's party. "I always keep my word," he was quoted as saying by the ANSA news agency.

The centre-left opposition, put into shambles by Berlusconi over the past two years, smelled blood. New opposition leader Dario Franceschini lashed out at the prime minister, asking indignantly whether Italians would want their children raised by a man like him.

The Berlusconi camp was quick to counterattack.

"I would be thrilled for Franceschini's children if they had a father like mine," shot back Marina Berlusconi, his oldest child and head of the Mondadori publishing house in her father's media empire.

The case has become a major test of whether Berlusconi can hold on to his popularity or is beginning to show the first cracks in his dominance of power in Italy.

Berlusconi won praise for the government's rescue effort during the April earthquake in the Abruzzo region, despite such dubious attempts at humour about the homeless having a beach vacation at the state's expense.

Berlusconi said his comments were meant to infuse the survivors with optimism - and indeed they were greeted with applause by those present, even if they raised eyebrows farther away.

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