The US called on Russia on Tuesday to rigorously investigate the murders of a human rights activist and her husband in Chechnya.
"It's important that the Russian government vigorously and immediately investigate these appalling crimes and bring those who are responsible to justice," US State Department spokesman PJ Crowley said.
The bodies of prominent activist Zarema Sadulayeva and her husband, Alik Djibralov, were found shot to death in the trunk of a car on Tuesday, one day after they vanished.
They are the latest of a string of attacks against human rights proponents. The US in the past has criticised Moscow for being too slow to thoroughly investigate murders of journalists or activists at odds with the Kremlin.
"We do have deepening concern about the violence of those who are advocating human rights, the rule of law, and independent media and humanitarian assistance in the North Caucasus," Crowley said.
"These kinds of murders have a chilling effect on freedom and respect of law within the society," he said.
Russian President Dmitry Medvedev, however, quickly called for an investigation by state prosecutors and the interior ministry.
The incident comes less than a month after the murder of Natalya Estemirova, another human rights activist operating in Chechnya, an incident which provoked a harsh outcry internationally.
Sadulayeva and her husband headed the non-governmental organisation Let's Save the Generation. The charity helps young people in the troubled southern Russian republic, which was ravaged by war between separatists and Russian forces in the 1990s.