A leading international human rights group is calling on Russia to "put a halt to the atmosphere of fear" in Chechnya following Wednesday's murder of acclaimed rights activist Natalya Estemirova.

Human Rights Watch called on Russian authorities to immediately investigate the activist's abduction and killing and bring those responsible to justice. Unidentified kidnappers grabbed Estemirova, a 50-year-old single mother, Wednesday in the Chechen capital, Grozny. Authorities found her body hours later in neighboring Ingushetia, with gunshot wounds to the head and chest.

?Natasha was one of the most hard-hitting researchers on human rights abuses in Chechnya,? said Allison Gill, a Human Rights Watch researcher based in Moscow. ?She was working on all of the most serious and sensitive human rights issues that exist there, including extrajudicial executions, punitive house burnings, torture, arbitrary detention, and illegal prisons.?

Gill said Estemirova did not want the world to forget Chechnya, a southern Russian republic that saw years of war between Russian forces and local separatists. The republic is headed by pro-Kremlin leader Ramzan Kadyrov, whose government Estemirova accused of human rights abuses.

?There have been serious and credible accusations that Ramzan Kadyrov, or forces loyal to him, have committed serious human rights abuses in Chechnya,? said Gill. ?These obviously need to be the subject of investigations.?

"There is serious and credible information that Ramzan Kadyrov personally threatened Natasha on several occasions,? she said. According to Gill, the Chechen leader had reasons not to like her work, because she was ?uncovering abuses carried out by his forces, or by forces loyal to him.?

Estemirova is the latest rights activist to die violently. Rights lawyer Stanislav Markelov and journalist Anna Politkovskaya were gunned down in separate attacks in Moscow in the past three years. Politkovskaya had worked closely with Estemirova on Chechen issues.