Two suspects have been detained in connection with the killing last month in Moscow of Russian opposition politician Boris Nemtsov.
Aleksandr Bortnikov, director of the Federal Security Service (FSB), said on Channel One on March 7 that Anzor Gubashev and Zaur Dadayev have been detained "on suspicion of committing the crime."
He said the suspects are residents of the Caucasus region, where Moscow has been fighting militarily against insurgency for decades.
Bortnikov said that Russian President Vladimir Putin had been informed of the arrests, and he added that the investigation is continuing.
A Moscow district court is expected to rule on March 8 whether to formally arrest and charge the suspects.
The head of Russia's Presidential Human Rights Council, Mikhail Fedotov, told Interfax it is important that those who ordered and organized Nemtsov's killing be brought to justice, as well as those who carried out the crime.
Ilya Yashin, an opposition ally of Nemtsov, told Interfax that he hopes the suspects are actually connected with the killing but that "it is too early to tell to what extent that is true." He said that authorities had not informed Nemtsov's political allies about the detentions.
Nemtsov's lawyer, Vadim Prokhorov, also told journalists he had not been informed, but he said the development is "good news."
Interfax quoted a lawyer for Anna Durytska, the Ukrainian model friend who was with Nemtsov when he was killed, as saying Durytska may be summoned from Ukraine for further questioning in light of the detentions.
Nemtsov, 55, was a former first deputy prime minister and staunch critic of Putin and of the war in Ukraine. He was shot to death near the Kremlin late on February 27. Opposition activists believe Nemtsov was killed because of his political activity, while Russian investigators are looking into several possible motives.
On March 4, Putin said "it is necessary to rid Russia of "shame and tragedies" such as Nemtsov's killing. He accused the opposition and "extremists" of sowing hatred in Russian society.
"We are encountering attempts to use so-called color technologies from the organization of illegal street protests to overt propaganda of hatred on social media," Putin said.
Critics, however, have blamed the Kremlin and Kremlin-friendly media outlets for the atmosphere of hatred.
"The atmosphere of mad aggression created by state television...has signaled that you could do anything to people expressing a different view," Dmitry Muratov, editor of the independent Novaya Gazeta newspaper, told AP on March 6.
A charismatic politician who spoke nearly flawless English, Nemtsov was an ardent proponent of liberal economic reforms and rose to national prominence as the popular governor of the Nizhny Novgorod region in the 1990s.
Once dubbed the “golden boy” of Russian politics in the media, Nemtsov was later named first deputy prime minister by Russian President Boris Yeltsin, a move that many interpreted as the Russian leader’s bid to groom his heir to the Kremlin.
He became a strident Kremlin critic with the rise to power of Vladimir Putin, a former KGB officer whom Yeltsin appointed to succeed him in a 1999-2000 New Year's speech.