A human rights group blamed Chechnya's president for the kidnap and murder of a prominent activist, the latest in a series of slayings of establishment critics in Russia, Reuters reported.
Natalia Estemirova, a close friend of murdered Russian journalist Anna Politkovskaya, worked for the human rights organisation Memorial in the Chechen capital Grozny and documented abuses by law enforcement agencies.
She was abducted on Wednesday morning in Chechnya, and her body was discovered later in woodland in neighbouring Ingushetia.
A Kremlin spokeswoman said President Dmitry Medvedev was "outraged" and had ordered an investigation.
Memorial's Chairman Oleg Orlov pointed the blame at Chechen President Ramzan Kadyrov, a former rebel turned Kremlin loyalist.
"I know, I am sure of it, who is guilty for the murder of Natalia... His name is Ramzan Kadyrov," he said in a statement on Memorial's website www.memo.ru late on Wednesday.
"Ramzan already threatened Natalia, insulted her, considered her a personal enemy."
Interfax news agency quoted Kadyrov as saying the perpetrators of her "monstrous" murder "deserve no support and must be punished as the cruellest of criminals".
The murder is the latest in a series of killings of journalists and human rights defenders in Russia which has drawn international condemnation and led to questions about Medvedev's pledges to uphold the rule of law and build a freer society.
"The body had two wounds to the head, it was clear she had been murdered in the morning," Madina Khadziyeva, a spokeswoman at the Ingush Interior Ministry, told Reuters.
Amnesty International and the New York-based Human Rights Watch (HRW) said she was shot.
Estemirova was a single mother aged about 50, friends said, and leaves a teenage daughter. She was snatched as she left her house, and cried out she was being kidnapped as she was shoved into a white vehicle and driven away, said Memorial colleagues and HRW.
"BRUTAL ACT"
"We of course condemn that brutal act and call for the authorities to try to establish who is responsible," said Swedish Foreign Minister Carl Bildt, whose country holds the European Union's rotating presidency.
"Natalia Estemirova's murder is a consequence of the impunity that has been allowed to persist by the Russian and Chechen authorities," said Irene Khan, Secretary General of Amnesty International.
Well known to diplomats and human rights activists in Russia, Estemirova was the inaugural recipient in 2007 of the Anna Politkovskaya Award, given by the charity Reach All Women in War (RAWinWAR).
Journalist Politkovskaya was gunned down by a lone assailant in her Moscow apartment building in 2006 as she returned home from a shopping trip. Nobody has yet been convicted of her murder.
Memorial said Estemirova's investigations into abductions, unlawful killings and public executions had sparked veiled warnings from authorities in Chechnya.
The mainly Muslim region was defeated in two separatist wars against Russia in the 1990s. With the nearby republics of Ingushetia and Dagestan, it still faces a simmering low-level Islamist insurgency.
Human rights groups have repeatedly accused the authorities of serious abuses including house burning, extra-judicial killings, torture and illegal punishment.
"It seems to be open season on anyone trying to highlight the appalling human rights abuses in Chechnya... Ensuring her murder does not go unpunished would help to break the vicious cycle of abuse and impunity in Chechnya," said HRW's director Kenneth Roth.