Stanislav Markelov, 34, had been at the forefront of legal attempts to block the early release of Russian Colonel Yuri Budanov, whose case had became a symbol of human rights abuses in Chechnya.

Markelov's body was found on Moscow's Prechistinkaya street, a 10-minute walk from the Kremlin, prosecutors in the Russian capital said. He had just finished giving a briefing to reporters.

"An assailant ran behind Markelov and a woman escorting him, Anastasia Baburova, and shot him in the back of the head from point-blank range. The woman tried to get hold of the suspect, but he shot her too," a law-enforcement source told local media.

The gunman escaped after the shooting.

Anastasia Baburova, a 25-year-old freelance journalist worked for the Russian opposition newspaper Novaya Gazeta, was shot in the head. She was rushed to the hospital in critical condition but has since died of her injuries, according to a spokeswoman for the newspaper.

Novaya Gazeta was also the newspaper which employed Anna Politkovskaya, the journalist and outspoken Kremlin critic murdered in 2006.

"It's terrible that this has become a greim reality of our life," said Karina Moskalenko, a lawyer for Politkovskaya's family. "This is a country in which murders of those defending human rights are now becoming everyday routine."

Tanya Lokshina, the deputy head of Human Rights Watch, called Markelov's killing as shocking as Politkovskaya's.

"For those in Chechnya, (Markelov's) name was a symbol of hope that you can find justice and the guilty will be punished," she said.

The editor-and-chief of Novaya Gazeta, Dmitry Muratov, said the paper had been able to recover a recording of Baburova's interview with Markelov that afternoon.

Abuses in Chechnya

Markelov became well known for fighting the early release of Yuri Budanov, a Russian colonel who was convicted in the murder of 18-year-old Elza Kungayeva in 2000. Her family said she had been raped and killed by drunken Russian troops.

Her death became a symbol of Russian human rights abuses there.

Budanov was convicted of the murder in 2003 and jailed for 10 years, the highest-ranking Russian officer to be imprisoned for war crimes in Chechnya.

His early release last Thursday triggered a wave of protests in mostly Muslim Chechnya.

Marklov had planned to appeal the case to the European Court of Human Rights in Strasbourg if Russia's Supreme Court refused to hear a new complaint against Budanov's early release.

The Interfax news agency reported that Kungayeva's father talked to Markelov on Friday and that the lawyer said he had been threatened with death unless he dropped the case.