'The militias had much to fear from her,' says the BBC's Rupert Wingfield-Hayes
Russian President Dmitry Medvedev has expressed "outrage" at the murder of a prominent human rights activist, Natalia Estemirova.
He has ordered an inquiry into the killing of Ms Estemirova, who was investigating alleged abuses by government-backed militias in Chechnya.
She was abducted and bundled into a van as she left her home in the Chechen capital, Grozny, on Wednesday.
Her body was found in neighbouring Ingushetia, with gunshot wounds.
Ms Estemirova, 50, had been gathering evidence - for the Russian human rights organisation, Memorial - of a campaign of house-burnings by government-backed militiamen.
She was known to be a fierce political opponent of Chechnya's government, led by pro-Moscow President Ramzan Kadyrov.
Accusation
In a strongly-worded statement, the head of Memorial, Oleg Orlov, linked the Chechen authorities to the murder of Ms Estemirova, alleging that she had been personally threatened in the past.
Mr Kadyrov, who has previously denied accusations of involvement in the killing of prominent Russian journalist Anna Politkovskaya, has not directly addressed Memorial's allegations.
But he publicly condemned the killing, saying the perpetrators of the murder "deserve no support and must be punished as the cruellest of criminals", Russian news agency Interfax reported.
There is no shred of doubt that she was targeted due to her professional activity
He said he would take personal control of the investigation.
In Washington, the White House issued a statement saying the US was "deeply disturbed and saddened by the... brutal slaying".
"Such a heinous crime sends a chilling signal to Russian civil society and the international community and illustrates the tragic deterioration of security and the rule of law in the North Caucasus over the last several months," said the White House.
'Sensitive' cases
Ms Estemirova had worked with the Anna Politkovskaya, who was shot dead in 2006, and the activist Stanislav Markelov, who was killed in January this year.
In 2007 she was awarded the inaugural Anna Politkovskaya Prize, and had also received awards from the Swedish and European parliaments.
New York-based human rights group Human Rights Watch (HRW) said Ms Estemirova had been working on "extremely sensitive" cases of human rights abuses in Chechnya.
"There is no shred of doubt that she was targeted due to her professional activity," said Tanya Lokshina, HRW Russian researcher in Moscow.
Campaign group Amnesty International said her murder was a consequence of the "impunity" allowed to persist by the Russian and Chechen authorities, and an attempt to gag civil society in the country.
'Most to fear'
BBC Moscow correspondent Rupert Wingfield-Hayes, who met Ms Estemirova in Chechnya just six weeks ago, says she was engaged in very important and dangerous work.
She was investigating hundreds of cases of alleged kidnapping, torture and extra-judicial killings by Russian government troops or militias in Chechnya.
Our correspondent says it was the government-sponsored militias that had most to fear from her work.
She is the most recent in a long line of human rights activists and lawyers to have been killed or attacked in Russia.
Our correspondent says the history of this type of case over many years is that very rarely are the killers brought to justice.
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