The U.S. and Ukraine condemned the killing of Russian opposition leader Boris Nemtsov, who was gunned down in Moscow on Friday. While Ukraine's President Petro Poroshenko said that with his death the "bridge between Ukraine and Russia" was lost, U.S. President Barack Obama called for a prompt investigation into the killing.  

"He was a bridge between Ukraine and Russia. The murderers' shot destroyed that. I think it was not coincidental. I do not doubt that the killers will be punished. Sooner or later," Poroshenko wrote on his Facebook page, according to Sputnik News. 

At least seven shots were fired at Nemtsov by attackers from a passing car, a representative of Russia's investigative committee probing the incident reportedly said. Russian President Vladimir Putin reportedly suggested that the incident bore signs of a contract killing.

Meanwhile, Obama asked the Russian government to conduct a prompt and impartial investigation into the incident.

"I admired Nemtsov’s courageous dedication to the struggle against corruption in Russia and appreciated his willingness to share his candid views with me when we met in Moscow in 2009.  We offer our sincere condolences to Boris Efimovich’s family, and to the Russian people, who have lost one of the most dedicated and eloquent defenders of their rights," Obama said, in a statement released by the White House on Friday.

"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," the statement read.

U.S. Secretary of State John Kerry also expressed shock at the Nemtsov's killing and urged authorities to conduct a detailed investigation into the incident.

"I am shocked and saddened to learn of the brutal murder of former Russian Deputy Prime Minister Boris Nemtsov in central Moscow," Kerry said, in a statement released Friday, adding: "The United States urges the Russian authorities to act expeditiously to investigate and bring to justice those responsible."