BREMMER: The outlook for US-Russia relations just reached a new low for the post-Cold War era

The killing of prominent Russian opposition figure and former deputy Prime Minister Boris Nemtsov on a bridge across the street from the Kremlin will have a chilling effect on Russia's opposition and on already frosty relations between the US and Russia, Eurasia Group president and international affairs analyst Ian Bremmer told Business Insider.

"Political consolidation in Russia and a deteriorating economy has made public opposition to the Kremlin far more dangerous," Bremmer explained by email. "The opposition may not be strong in Russia, but Nemtsov has long been one of its most articulate and outspoken proponents."

A Russian regional governor at just the age of 32, Nemtsov became one of Russia's most well-known reformists, organizing the opposition to Putin and leading investigations into high-profile cases of corruption - like during preparations for the 2014 Winter Olympics in Sochi.

But Nemtsov's long career both inside and outside the Kremlin and international stature wasn't enough to protect him. "He's just paid the ultimate price," wrote Bremmer. "The outlook for US-Russia relations has just reached a new low for the post-Cold War era.

"The Kremlin has been digging in for what they see as a complete break of the US-Russia relationship," Bremmer added. "Whoever is behind the assassination, it sends a deep chill across the Atlantic."