Russian security officials say they have arrested six people suspected of involvement in the assassination of a liberal member of parliament.

Galina Starovoitova, a prominent MP and close ally of former President Boris Yeltsin, was gunned down late on 20 November, 1998, on the staircase of her apartment block in St Petersburg.

Four of the arrested have been charged, according to the regional office of Russia's Federal Security Service (FSB).

The murder caused outrage in Russia

Several wanted suspects are still at large.

FSB officials say the suspects are members of a criminal gang with regional connections.

The arrests were sanctioned by a judge instead of a prosecutor, in accordance with new arrest proceedings.

Police have interviewed more than 1,000 witnesses and conducted at least 40 searches in the four year investigation into Ms Starovoitova's murder.

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The only witness to the killing, her personal assistant Ruslan Linkov, was himself critically wounded but survived.

Although Ms Starovoitova had been involved in some business dealings, Mr Linkov insisted it was a political murder.

The killing caused outrage in Russia and abroad.

Galina Starovoitova said she was getting death threats

US President Bill Clinton called the murder an assault on the country's efforts to build a society based on the rule of law.

Many journalists at the time said Russia has lost its icon of democracy.

Although Ms Starovoitova was a close ally of President Yeltsin, she was said to be getting increasingly disillusioned with his leadership.

She said she had been getting death threats and that her telephone was being bugged by the security services that she so often criticised.

St Petersburg, home town of current Russian President Vladimir Putin, has acquired a reputation as a magnet for contract killers.

As well as the assassination of Ms Starovoitova, regional deputy governor Mikhail Manevich and businessmen and bankers have been murdered in the city.