By Alan Baldwin

RIO DE JANEIRO (Reuters) - Irish bantamweight Michael Conlan blasted Olympic boxing body AIBA as 'corrupt' on Tuesday in an expletive-laden rant at the judging after losing to Russia's Vladimir Nikitin in the quarter-finals.

Saying he had been robbed of a rightful win, and vowing never to fight again in any AIBA-organized competition, the world champion also accused Russia of influencing judges.

"AIBA are just corrupt. They've robbed me of my Olympic dream," he told reporters after losing on points in a unanimous decision that, to some observers, seemed at odds with what they had witnessed.

"Obviously Russia can't dope this time so they are obviously paying the judges a lot more," he added.

"I will never box an AIBA competition again. Not APB, not WSB, not world championships or Olympic Games. Corruption runs deep... I just think they are rotten to the core."

An AIBA spokesman said Conlan was a champion who came to Rio with high expectations and was understandably disappointed to have lost.

"Afterwards, it's his personal judgement," he said. "All I can say is that AIBA is striving for a fair, level playing field.

"The idea is not to benefit one country towards another, we represent 200 national federations. These statements are groundless but he's free to have his opinion."

Russian officials said the judging had to be respected and boxers should show dignity in defeat.

"The Russians are constantly being accused of something. Let's deal with these things in a dignified way," said Igor Kazikov, head of the Russian delegation at the Games.

"There were judges sitting there, professionals who take responsibility for these things. Why is there this mistrust all the time?"

Dozens of Russian athletes, including virtually the entire track and field team, were suspended as part of sanctions against the country for a systematic state-backed doping program that included the Sochi 2014 Winter Olympics.

Russian heavyweight Evgeny Tishchenko was booed when he won gold on Monday.

NEW SYSTEM

The scoring system has been changed for Rio from a computerized system to a professional-style, 10-point one.

Conlan, who had been the last Irish boxer left in the tournament, lost 28-29 on all three scorecards.

The three judges -- from Brazil, Sri Lanka and Poland -- all gave Conlan the second round 10-9 10-9 10-9 but scored the first and last in favor of his rival.

"I was boxing the ears off him, I don't know how it went against me," said Conlan, who lingered in the ring after the fight, twirling his vest around his head to applause from the crowd. He also gave the judges a piece of his mind.

"I thought the first round I won easy by boxing him. Second round I completely annihilated him standing in close to him. Third round the same, probably a bit closer than the second. I put a serious shift in.

"He was completely surprised (to win). He roared like he'd won the Olympic gold... He knows he didn't win. The American kid's going to pick him to shreds and I wouldn't be surprised if they rob him too."

Nikitin will fight highly-rated Shakur Stevenson in the semi-finals, with both guaranteed at least bronze medals.

U.S. coach Billy Walsh, who is Irish, joined in the criticism after his light-welterweight Gary Russell missed out on a medal when a split decision went to Uzbekistan's Fazliddin Gaibnazarov.

"The judging has been atrocious," he told reporters. "The last time I saw it as bad was in Seoul in 1988 when Roy Jones got robbed in the final.

"I saw Michael Conlan's first two rounds in the changing area and he completely out-boxed this guy. He out-fought him in the second round and out-boxed him in the first. And he didn't get it."

(Additional reporting by Jack Stubbs and Mark Trevelyan; Editing by Clare Fallon)