Populist leader Vladimir Zhirinovsky's Liberal Democratic party wants the 38-year-old kicked out of the State Duma lower house for his "anti-state" vote, A senior member had to remind Zhirinovsky later that deputies cannot be expelled simply for the way they vote.

Ponomaryov says last week's vote, and the hostility towards him, shows there is no room for independent thought in a parliament that is dominated by the centre-right United Russia party, which is loyal to President Vladimir Putin.

"Everyone is afraid of acting against the center-right now because they are afraid of being victims of political repression," Ponomaryov, who represents the centrist Just Russia party but says he is independent, told Reuters in an interview.

Ponomaryov won little support when he tried to explain his decision on Twitter. Someone writing under the name of "studenth" posted a reply saying he had "spat poisonous saliva" and that 99 percent of the population would want to crucify him.

All the other 443 deputies who voted in the Duma last Thursday backed annexing the Black Sea peninsula from Ukraine, standing afterwards for the national anthem. The Federation Council upper house unanimously approved bringing Crimea into Russia, a process which has led to the deepest crisis in relations between Moscow and the West since the Cold War.

Ponomaryov said he had voted against annexing Crimea because it could result in "large-scale bloodshed in Europe".

"(It) is destabilizing the entire system of international relations and international security that has been established," he said. "Our current actions are provoking a war."

It is not the first time Ponomaryov, a physicist and businessman who once worked at the now defunct oil company Yukos, has opposed Putin's will.

He was an organizer of street demonstrations against Putin in the winter of 2011-12 and was censured by parliament in 2012 for calling United Russia a "party of swindlers and thieves", a phrase coined by another protest leader. He has also been in trouble for not dressing formally enough in the Duma.

Ponomaryov says annexing Crimea is not in Russia's interests because it will drive Ukraine into the arms of former Cold War foe NATO and that leaders in Kiev benefit from Moscow's hostility.

"The only way for them to survive with a worsening economy is a wave of patriotic sentiment," he said. "The more evidence there is of Russian aggression, even if it's fake, the more (support) they can mobilize."

Outside parliament, Ponomaryov is not entirely alone. A prestigious Russian state university said on Monday it had sacked a philosophy professor for comparing Moscow's actions with Nazi Germany's annexation of Austria in 1938.

Former Yukos owner Mikhail Khodorkovsky, who spent more than a decade in jail and lost his company after falling out with Putin, has also attacked the Kremlin over its Ukraine policy. .

Ponomaryov said Russia had had no clear strategy since the overthrow of Moscow-backed Ukrainian president Viktor Yanukovych last month.

"Putin bet on Yanukovych, Yanukovych was ousted, and now he wants to show he was right by turning things to his advantage," Ponomaryov said. "Russia's response to these events is not part of a thought-out strategy but rather a reaction to events in Ukraine. A mainly emotional reaction."