Anna Politkovskaya, a prominent Russian journalist known as a fierce critic of the Kremlin's actions in Chechnya, has been found dead in Moscow.
Politkovskaya had often received threats
The 48-year-old mother of two was found shot dead in a lift at her apartment block in the capital.
A pistol and four bullets were found near her body and a murder investigation has been launched.
Ms Politkovskaya's murder has all the hallmarks of a contract killing, says the BBC's Emma Simpson in Moscow.
The award-winning journalist became ill with food poisoning on her way to report on the Beslan school siege in 2004, which some believed to be an attempt on her life.
Ms Politkovskaya, who worked for the newspaper Novaya Gazeta, was known for exposing rights abuses by Russian troops in Chechnya.
She also acted as a negotiator with the Chechen rebels who held a siege in a Moscow theatre in 2002.
The head of Russia's journalism union described her as the conscience of the country's journalism.
She was one of the few remaining high-profile, independent journalists in Russia - and her death will cause widespread anger and shock, says our Moscow correspondent.
"Russia has lost a brave and dedicated human rights defender," said Nicola Duckworth from the rights group Amnesty International.
Ms Politkovskaya "spoke out fearlessly against violence and injustice, and campaigned tirelessly to see justice done".
Amnesty International has called for a thorough investigation into the killing but Russian political analyst Anna Zelkina is doubtful there will be results.
"There is this series of politically motivated murders like hers," she told the BBC.
"I'm afraid that there will be less and less people who would be taking the risk to report... [she's] a very difficult person to replace."
Ms Politkovskaya was killed at around 1630 local time (1330 GMT), Dmitry Muratov, editor in chief of the Novaya Gazeta said.
RUSSIA'S CONTRACT KILLINGS
Sept 2006 - first deputy chairman of Russia's central bank Andrei Kozlov shot dead in Moscow
Oct 2005 - former bank head Alexander Slesarev gunned down near Moscow
July 2004 - US editor of Forbes' Russian edition Paul Klebnikov shot dead in Moscow
Oct 2002 - Magadan governor Valentin Tsvetkov killed in Moscow
Nov 1998 - liberal MP Galina Starovoitova killed in St Petersburg
March 1995 - leading journalist Vladislav Listyev shot dead in Moscow
Vitaly Yaroshevsky, deputy editor of the newspaper, believes she was killed because of her work.
"The first thing that comes to mind is that Anna was killed for her professional activities. We don't see any other motive for this terrible crime," he told the Reuters news agency.
Moscow deputy prosecutor Vyacheslav Rosinsky has said investigators are considering the link between the journalist's death and her work.
"We think that one of the leads of Politkovskaya's intentional homicide is her public duty," he told Russian agency Itar-Tass.
Oleg Panfilov, director of the Moscow-based Centre for Journalism in Extreme Situations, said Ms Politkovskaya had frequently received threats.
"There are journalists who have this fate hanging over them. I always thought something would happen to Anya, first of all because of Chechnya," he told the Associated Press news agency.
A murder investigation is under way
"Whenever the question arose whether there is honest journalism in Russia, almost every time the first name that came to mind was Politkovskaya," he added.
In 2001, she fled to Vienna, Austria, after receiving e-mail threats claiming a Russian police officer she had accused of committing atrocities against civilians wanted to take his revenge.
In an interview two years ago with the BBC, Ms Politkovskaya said she believed it was her duty to continue reporting, despite receiving such death threats.
"I am absolutely sure that risk is [a] usual part of my job; job of [a] Russian journalist, and I cannot stop because it's my duty," she said.
"I think the duty of doctors is to give health to their patients, the duty of the singer to sing. The duty of [the] journalist [is] to write what this journalist sees in the reality. It's only one duty."
What is your reaction to the news of Anna Politkovskaya's death?
This is terrible news. A few years ago I read her work "Putin's Russia" and her warmth and passion for Russia came through in every story. This may well be another indication that the Russian transition will prove not to result in a democratic outcome.James McCormick, UK
That is brutal. Certainly, there are no doubts concerning the cause of the murder (and a fact that it was a murder); assuredly, nothing would be done, nothing would be clear and the case would initially be forgotten with a few TV documental films as an epitaph. Of course, sometimes she should not have been that straight, at least not with names when publishing her articles. Finally, her children - poor kids, they lost their mother for the truth.Marat Khisamov, Russia
Coming from a Russian family and having re-visited my roots there, I am shocked and dismayed. However, this sort of blithe disregard for human life will always be endemic in a country still run by fear, and by a man who's KGB heritage is still all too present. Nick Francis, UK
I am appalled by the murder of Anna Politkovskaya. I have read quite a few of her books and I always wondered how she got away with it. Indeed, nothing has changed and if someone is in the way, just eliminate them. No respect for human life, children, freedom of speech, despite the cosmetics of change in Russia. May she rest in peace and her children remember her for the courageous woman that she was. Anne Popoff, Canada
Mr Putin takes pride in his reputation as a strongman, and bangs on about law and order - yet in his own capital a central banker and a leading journalist have been gunned down in the space of a month, and I'm sure the killers will never be found. The Russian authorities are doing a great job hounding the Georgians but contract killers need not worry. Ivan, Ukraine
Ms. Politkovskaya was one of the very few who stood for what she believed in, despite of the constant threat involved in her role. The array of possible suspects in her murder is long, reflecting not just the range of her inquiring mind but also the extent of greed, theft and violence in a society still groping for an accommodation between capitalism and the rule of law. Her death is Russia's loss. May god bless her soul. Apoorv Vyas, Ireland
She was an extremely gifted woman dedicated to her field of work and not afraid of exercising what we Americans call Freedom Of speech. I could only hope that true democracy will one day reign over Russia. As Einstein said "Great spirits always encounter violent opposition from mediocre minds."Hector Troncoso, US
I am in absolute shock. Anna was an extraordinary person of an unmatched integrity and drive. Being born Russian, I love Russia with all my heart. This news of a cold blood murder makes me so angry. Can this great country be ever free? Such loss, such emptiness. Arina Kurchina, UK
I'm always amazed by the bravery of journalist who carry on reporting the truth despite threats and intimidation. It saddens me that she isn't the first, and won't be the last, journalist to die for her integrity. For her families sake, as well as the sake of truth, I hope there is a full and fair investigation into her death. Katherine, London
It is a criminal act on the life of such a renounced journalist. She died for the truth through her profession. People grow annoyed when they are hit by the truth. She is gone for ever and it's a big loss to her family and the nation. Always remember her good work! David M.G Vandi, Sierra Leone
I'm totally gutted to hear this news. She was part of a great tradition of courageous war reporting and investigative journalism who have never been afraid to put their lives on the line in pursuit of the truth. Russia's war in Chechnya is the dirtiest of wars and Russian politics is equally dirty these days. I fear that nothing will change for a long, long, time. Harvey Burgess, US
I am broken-hearted that this relentless journalist has been taken away from us and I am driven deeper into a perception of Russia as a darkening state. Sheryl Feldman, US
I am very sad about her murder. Anna was a journalist, who wasn't frightened into silence about the Chechnya war. Pekka Salo, Finland
I am almost sure the real killers will never be found, at least not within the lifetime of the present Russian authorities. This courageous woman saved the honour of Russia. Let her rest in peace. Marek Porzycki, Poland
I am truly sorry for the death of the Journalist. I think all those having problems with the principles of democracy and free society resort to guns at the end of the day. This is terrible news and I think it clearly shows how the current administration views freedom of expression. Who would possibly want to kill a journalist? I think the world organisations working in relation to journalism should condemn this horrible act. Abraham, Ethiopia
I think it is terrible that someone so dedicated to stopping abuse of human rights and providing honest reporting could be killed so brutally.Allison Nastoff, US
It seems that Russia is back in the old days of the Iron curtain. Those who oppose their views are eliminated.Francisco Schnell, Portugal
This is wrong. A reporter does her job, reporting facts and reporting atrocities committed during the Chechen conflict. Not to die in conflict but to be found dead in a lift because someone don't like what she has written. We can not change freedom of press and reporters will have to go on reporting, we can not bow down to these people. Joseph Ivanov, Canada