Washington is deeply saddened with the news of lethal attack on family members of late Russian human rights activist Maksharip Aushev, the U.S. Department of State said.

"The United States is deeply saddened by reports that four family members of late human rights defender Maksharip Aushev were victims of a car explosion in Nazran, Ingushetia," Ian Kelly, a spokesman for the U.S. Department of State, said.

Aushev's 51-year-old mother-in-law and one of his brothers-in-laws were killed in a car blast, which occurred in Ingushetia's largest city of Nazran last Wednesday. His 27-year-old widow and another brother-in-law were also injured.

"The State Department posthumously honored Mr. Aushev with its Human Rights Defenders Award earlier this month, for his work shining a spotlight on human rights abuses in Russia's North Caucasus. We offer our condolences to Aushev's family and his colleagues who will carry on his courageous advocacy for human rights," he said.

Investigators say a bomb was planted under the driver's seat and detonated by remote control. The force of the explosion was estimated as equivalent to 5 kg of TNT.

"We look to the Russian Government to conduct a prompt and full investigation. We remain concerned about the increasing incidence of violence in the North Caucasus," Kelly added.

Aushev worked before his death with Ingush opposition journalist Magomed Yevloyev, who was shot dead after being taken into police custody in the republic in 2008. A police officer was recently jailed for two years for "accidental homicide" in connection with the shooting.

After Yevloyev's death, Aushev ran his website, which was critical of local authorities.

In October, Aushev's car was attacked by assailants armed with automatic weapons in the neighboring republic of Kabardino-Balkaria. He died at the scene.

Russia's North Caucasus republics have been plagued by violence this year. On August 17, at least 20 people were killed and 260 injured in a suicide truck bombing on a police compound in Nazran.

In June, Ingush President Yunus-Bek Yevkurov survived a car bomb attack on his motorcade.

MOSCOW, December 22 (RIA Novosti)