By Alexei Anishchuk and Steve Gutterman

MOSCOW (Reuters) - One of Russia's most prominent reputed crime bosses, a 75-year-old nicknamed "Grandpa Hassan" who survived time in Soviet jails and assassination attempts, was shot dead on a Moscow street on Wednesday in what may have been a turf war, authorities said.

After the criminal chaos that characterized the 1991 break-up of the Soviet Union, President Vladimir Putin has claimed credit for bringing order to Russia since he rose to power in 2000. But Kremlin critics say corruption has worsened and contract killings on city streets continue, if less frequently.

An unidentified gunman hit Georgian-born Aslan Usoyan with a single bullet and he died shortly afterward in hospital, the federal Investigative Committee said. It said a woman at the scene suffered two gunshot wounds.

A Committee statement said six 9mm bullet casings were found on a stairwell between the fifth and sixth floors of a building across the street from where Usoyan was hit, suggesting the gunman fired from there.

Authorities, it said, were conducting ballistics tests and considering potential motives "connected to the criminal activity of the victim and possible conflicts with other representatives of the same milieu."

Usoyan was shot in the head outside a restaurant, Interfax news agency reported, citing a police official it did not name.

The midafternoon killing on a snowy street about 1 km (half a mile) from the Kremlin ended a life of alleged crime that began with a conviction in then-Soviet Georgia, for resisting police, when Usoyan was 19 years old.

He later served terms for crimes including theft and "speculation" - essentially selling at a profit, which was often illegal and under close scrutiny in the communist Soviet Union.

He earned the underworld title of "vor v zakone" - or thief in law - meaning a criminal godfather.

After the Soviet Union disintegrated in 1991, there were almost daily killings across Russia as criminal gangs battled to gain control of lucrative businesses and carve up territory.

According to Russian media reports, in the years after the Soviet collapse Usoyan headed a crime network involved in illegal gambling, drug and weapons sales, and natural resources extraction, with stakes in former Soviet republics and beyond.

CONTRACT KILLINGS

Usoyan survived a contract hit in September 2010 when a gunman shot him in the stomach as he got out of his car near his apartment on Moscow's main street. Media reports at the time linked that shooting to a conflict between crime groups.

The Investigative Committee said Usoyan had survived more than one assassination attempt.

His killing echoed that of criminal boss Vyacheslav Ivankov, known as Yaponchik, whose saga also spanned the communist and post-Soviet eras but included jail in the United States on extortion charges.

Ivankov had tried to mediate in Usoyan's reported conflict with another reputed crime figure but was shot in the stomach by a sniper in Moscow in July 2009 and died that October.

That same year, Usoyan said that he had left organized crime behind him. He told a interviewer he was "far from all that", referring to the criminal world, and that he lived on a pension, according to a transcript published by newspaper Komsomolskaya Pravda.

Asked whether he lived on his pension alone, Usoyan gave a wry reply that translates as: "Kind of, yes."

(Editing by Mark Heinrich)