MOSCOW - Russia said Saturday it had arrested two men suspected of organising and carrying out the murder of opposition activist Boris Nemtsov, who was gunned down near the Kremlin in a brazen assassination that shocked the country.
The arrests come a week after the longtime critic of President Vladimir Putin was shot four times in the back as he strolled with his girlfriend along a bridge in the heart of the capital, in view of the Kremlin and Red Square.
"As a result of work that has been done, two men suspected of committing this crime were arrested today. They are Anzor Gubashev and Zaur Dadayev, and the head of state has been informed," the head of the FSB federal security service Alexander Bortnikov told state television.
He said the two men were from the Caucasus region.
A spokesman for the powerful Investigative Committee, Vladimir Markin, told Interfax news agency that the men were suspected of having "organised and carried out the assassination of Nemtsov," dispelling theories they had only been paid hitmen.
The latest killing of a high-profile government critic under Putin's rule prompted an outpouring of international condemnation and stunned members of an opposition who blamed the Kremlin for whipping up hatred against anyone who expresses dissent through state media who regularly refers to them as "traitors".
The 55-year-old, a renowned anti-corruption crusader who served as Boris Yeltsin's first deputy prime minister in the 1990s, was shot dead just two days before he was to lead a major anti-government rally.
However the protest march -- called to denounce Russia's alleged role in the Ukraine crisis -- instead became a massive memorial for Nemtsov, with tens of thousands swarming the streets of Moscow in the largest opposition gathering since a wave of anti-Kremlin protests in 2011-12.
Putin, whose rule has seen the steady suppression of independent media and opposition parties, had promised an all-out effort to catch those responsible for an act which he called a "provocation".
Russian news agencies reported that the men were being held in the high-security Lefortovo prison in Moscow, and would appear in court by Monday at the latest to determine whether they should remain in custody.
Nemtsov's Ukrainian girlfriend Ganna Duritska, the sole witness to the murder, returned to Kiev after the killing.
Her lawyer Vadim Prokhorov told Kommersant radio he was unsure whether she would be summoned back to Moscow after the arrests but was "ready to cooperate" with investigators.
Theories over killing
Theories have proliferated since the killing over why Nemtsov was targeted.
Some suggest he was assassinated for criticising Russia's role in the Ukraine conflict, others for his condemnation of January's killings at the Charlie Hebdo satirical weekly in Paris by Islamist gunmen.
Friends said Nemtsov had been working on a report containing what he described as proof of Russian military involvement in the bloody uprising by pro-Moscow militias in eastern Ukraine.
Meanwhile investigators suggested the killers wanted to destabilise Russia, which is facing its worst standoff with the West since the Cold War over Ukraine, and Putin's allies also hinted at a Western plot.
Following the arrests Interfax cited an unnamed source close to the case as saying: "The trail of this crime may lead abroad. This theory is being actively considered."
The former head of the FSB -- the successor to the Soviet-era KGB -- and now lawmaker Nikolay Kovalev earlier told the RIA Novosti agency that initial information showed the two men were merely paid hitmen.
Former prime minister turned opposition leader Mikhail Kasyanov said he was pleased with the news that arrests had been made and told Interfax that investigators "should work in this direction," referring to finding others who may have been involved in organising the crime.
A fellow opposition activist, Ilya Yashin, welcomed the development but called for more information on the men's identities.
"We hope the arrest... is not an error but the result of good work by security forces, but for now it is hard to say," Yashin told Interfax news agency. "Quite frankly the execution of the investigation had not inspired any optimism, but the fact that there have been arrests inspires some optimism."
Nemtsov, a charismatic orator who was one of the last outspoken opponents to Putin, was a key speaker at mass opposition rallies against Putin's return to the Kremlin in 2012.
He wrote several reports critical of corruption and misspending under Putin.
In 2013, he said up to $30 billion of the estimated $50 billion earmarked for the Olympic Games that Russia was to host in Sochi had gone missing, which the Kremlin denied.
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