German Chancellor Angela Merkel has expressed shock at Wednesday's abduction and murder of acclaimed Russian human rights activist Natalya Estemirova.

Germany's Angela Merkel (R) and Russia's Dmitry Medvedev (L) at a news conference in Munich suburbs in southern Germany, 16 Jul 2009

Speaking after talks in Munich with visiting Russian President Dmitri Medvedev, the German leader called on Russia to clarify the circumstances of the murder.

Mr. Medvedev said he believes the murder was related to Estemirova's human rights work. He pledged a thorough investigation and vowed that her death will not go unpunished.

Several men kidnapped 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.

Estimirova had collected evidence of kidnappings, torture and killings in Chechnya since the start of the second separatist war there in 1999.

Officials of Russia's Memorial organization, where Estemirova worked, put the blame for her killing on pro-Kremlin Chechen leader Ramzan Kadyrov.  

Kadyrov said Thursday he would personally oversee the murder probe.  But a leading international rights group, Human Rights Watch, said only an independent probe will have credibility.

Russian human rights activist Natalya Estemirova (2007 file)

Estemirova was killed on the same day as the release of a report she helped research that itemizes evidence of ongoing criminal activity in Chechnya.  The Associated Press said the report by the Russian-Chechen Friendship Society concluded that Russian officials should be held accountable for crimes committed in the republic on their watch.

Meanwhile, Human Rights Watch, in a statement, called on Russia to "put a halt to the atmosphere of fear" in Chechnya following the murder. The group referred to violence in southern Russia as a "vicious cycle of abuse and impunity."

Estemirova had worked with other top rights activists, including rights lawyer Stanislav Markelov and journalist Anna Politkovskaya.  Both Markelov and Politkovskaya, who researched and wrote extensively about rights abuses in Chechnya, were gunned down in separate attacks in Moscow over the past three years.  No one has been convicted in either killing.

Estemirova's death sparked protests from the U.S. State Department and governments across Europe. A U.S. statement praised her "uncompromising ... willingness" to reveal the truth about human-rights abuses, especially in Chechnya, "regardless of where that might lead."

Swedish Foreign Minister Carl Bildt, whose country currently holds the European Union presidency, said the EU condemns what it called a "brutal act."

In 2007, Estemirova was awarded the first annual Anna Politkovskaya Award, in honor of her colleague and friend. The prize was created by the group, Reach All Women In War, with the support of female laureates of the Nobel Peace Prize.

Some information for this report was provided by AFP, AP and Reuters.