Kadyrov took power in Chechnya after his father was assassinated
The Russian-backed Chechen president, Ramzan Kadyrov, has vowed to hunt down the killers of prominent human rights activist Natalia Estemirova.
Ms Estemirova, a fierce Kadyrov critic, was investigating alleged abuses by government-backed militias in Chechnya when she was abducted and shot.
Colleagues of Ms Estemirova have blamed Mr Kadyrov's government for her death.
But the Chechen leader vowed to bring her killers to justice, describing Ms Estemirova as a "helpless woman".
Mr Kadyrov is a controversial figure who has brought relative calm to Chechnya after years of conflict, but human rights groups accuse his militias of widespread abuses.
Ms Estemirova's organisation, Memorial, had been investigating hundreds of cases of alleged kidnapping, torture and extra-judicial killings by Russian government troops or militias in Chechnya.
Mr Kadyrov himself was quick to denounce Natalia Estemirova's killers.
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.
Chechen militias were said to have much to fear from Estemirova's work
His spokesman, Alvi Kerimov, told the Associated Press news agency that the Chechen president would launch two investigations: one official and one unofficial, following Chechen traditions. He gave no further details.
But Mr Kadyrov's outrage was dismissed as a sham by Memorial's chief, Oleg Orlov, who said in a strongly-worded statement that the Chechen authorities were linked to the murder of Ms Estemirova.
Mr Orlov alleged that she had been personally threatened in the past and said Mr Kadyrov considered the activist a personal enemy.
The Chechen president, who took office in 2007, is descended from one of Chechnya's oldest and most respected clans and is a veteran of Chechnya's long conflict.
He is the son of Akhmad Kadyrov, a former Chechen rebel leader who became its Russian-backed president before being killed in a bomb attack in 2004.
He has often been accused by critics of a role in the 2006 murder of Russian investigative journalist Anna Politkovskaya, something he has repeatedly denied.
Natalia Estemirova 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.
Reaction to her killing was swift and strong, with Russian authorities, the White House and human rights organisations all condemning her murder.
Russian President Dmitry Medvedev expressed "outrage" and ordered an inquiry while in Washington, the White House issued a statement saying the US was "deeply disturbed and saddened by the... brutal slaying".
The heads of Amnesty International and Human Rights Watch both condemned the killing and expressed concern at the dangers faced by campaigning journalists and activists in Russia.
"It seems to be open season on anyone trying to highlight the appalling human rights abuses in Chechnya," said Kenneth Roth, director of New York-based group Human Rights Watch.
"It's high time the Russian government acted to stop these killings and prosecute those responsible."
Ms Estemirova had worked with the Anna Politkovskaya 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.
Human Rights Watch said Ms Estemirova had been working on "extremely sensitive" cases of human rights abuses in Chechnya.
"She documented the most horrendous violations, [and] mass executions," said Tanya Lokshina, HRW Russian researcher in Moscow.
"There is no shred of doubt that she was targeted due to her professional activity,"
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.