A masked gunman has killed a human rights lawyer who exposed one of the most notorious cases of abuses by Russia's army in Chechnya, together with a journalist who died later in hospital.

Law enforcement sources confirmed that lawyer Stanislav Markelov had been gunned down on a busy street in central Moscow, while a woman, Anastasiya Baburova, was hospitalised with a bullet wound to the head.

The opposition newspaper Novaya Gazeta confirmed the death of the 25-year-old intern reporter Baburova in hospital on Monday evening.

"The doctors did everything in their power. A few minutes ago, Novaya Gazeta journalist Anastasiya Baburova died," the paper said on its website.

Following the lawyer's death, the prosecutor's investigative department said: "The investigation is studying various theories on the killing, including a link to the deceased's professional activities."

Ms Baburova had written a number of reports on Russia's growing problem of racism and ultra-nationalism for Novaya Gazeta, the paper of the campaigning journalist Anna Politkovskaya, who was assassinated in 2006.

Human rights campaigner Lyudmila Alexeyeva, who heads the Moscow Helsinki Group, said: "The murder in the centre of Moscow of a man, of a lawyer involved in cases of political importance, has as much significance as the assassination of Anna Politkovskaya."

Mr Markelov and Ms Baburova had just emerged from a press conference given by Mr Markelov on the latest turn in the case of Elza Kungayeva, the 18-year-old Chechen whose 2000 strangling by Russian army colonel Yury Budanov became a cause celebre, highlighting systematic abuse by the Russian army in the war in Chechnya.

Budanov was released from jail on Friday after serving most of his 10-year sentence for the young Chechen woman's murder.

Mr Markelov had vowed to challenge the granting of early release to Budanov, who was convicted in 2003 after pressure for a conviction by human rights activists, while ultra-nationalists had rallied to his side.

- AFP