Obama condemns killing of Russia's Nemtsov

"The United States condemns the brutal murder of Boris Nemtsov, and we call upon the Russian government to conduct a prompt, impartial, and transparent investigation into the circumstances of his murder and ensure that those responsible for this vicious killing are brought to justice," Obama said in a statement, according to Reuters.

Obama met Nemtsov during a 2009 trip to Moscow, where he held talks with opposition parties after a meeting with then-President Dmitry Medvedev. Obama said he admired Nemtsov's "courageous dedication to the struggle against corruption in Russia."

With Nemtsov's death, Obama said, Russians have lost "one of the most dedicated and eloquent defenders of their rights."

"Nemtsov was a tireless advocate for his country, seeking for his fellow Russian citizens the rights to which all people are entitled," Obama said.