By Carol J. Williams and Sergei L. Loiko
February 27, 2015

Leading Russian opposition politician Boris Y. Nemtsov, a former first deputy prime minister under President Boris Yeltsin, was shot dead on a Moscow street near the Kremlin early Saturday, Russian officials and news agencies reported.

A fierce critic of Russian President Vladimir Putin, Nemtsov had been preparing to join an opposition rally Sunday against the Kremlin leader’s backing of separatists in eastern Ukraine, which has brought international sanctions against Russia and sent its economy into a tailspin.

“An unknown person shot and killed Boris Nemtsov on St. Basil’s slope by four shots from a handgun,” the Tass news agency quoted an unnamed official as saying. “A team of operatives and investigators is working at spot of the crime.”

The Russian Interior Ministry, which oversees police and security operations, later confirmed that Nemtsov had been gunned down in the shadow of St. Basil’s Cathedral on a sidewalk across the street from Red Square.

Television and YouTube video from the scene showed the lifeless body of the 55-year-old politician — once considered a future Kremlin leader — sprawled on a sidewalk along the busy thoroughfare in the heart of the Russian capital.

Putin expressed condolences to the family of the slain politician, his spokesman Dmitry Peskov said.

“Putin noted that this was a cruel murder and bears all the signs of a contract killing which appears exclusively provocative,” Peskov told ITAR-TASS.

Nemtsov ran afoul of Putin’s Kremlin administration years ago and had been active with the opposition coalition PARNAS.

Ilya Yashin, another leader of PARNAS, the most vocal opposition group in Russia, confirmed Nemtsov’s death to the RIA Novosti news agency.

A companion who witnessed Nemtsov’s killing was being questioned by police, the official Sputnik news agency reported.

Russia Today television, a pro-Kremlin mouthpiece, said on Twitter that the slaying “could be a provocation,” suggesting that the opposition was responsible for the killing to tarnish the Putin administration.

Pro-democracy allies and world leaders who knew the gregarious and energetic politician expressed horror over the killing that many were inclined to see as an assassination.

“Shock. Boris has been killed. It’s impossible to believe,” Ukrainian President Petro Poroshenko said via Twitter. “I’m certain the killers will be punished. Sooner or later.”