MOSCOW - Five men from the Caucasus region of southern Russia were brought Sunday before a Moscow court where two were charged for their alleged roles in the killing of Kremlin critic Boris Y. Nemtsov.

One suspect, former Chechen police commander Zaur Dadayev, pleaded guilty to the murder charge, Tass news agency reported. "Dadayev's involvement is confirmed by his confession," Judge Natalya Mushnikova of the Basmanny district court was quoted as saying after the arraignment.

Charges were also brought against Anzor Gubashev, who was arrested Saturday in the Ingushetia region of the Caucasus. Three others were ordered held for further investigation, court press secretary Anna Fadeyeva said.

Officials of the Federal Security Service and from Ingushetia identified three men arrested in the case and alluded to a fourth. But it was only when the suspects were delivered for their court appearance that the fifth man's implication was alleged.

"The Investigative Committee is requesting that five suspects involved in the murder of Boris Nemtsov be arrested. The investigation is ongoing," Russian Investigative Committee spokesman Vladimir Markin said via Twitter.

Under Russian law, a court must approve holding suspects without charges within 48 hours of arrest. Prosecutors sought and received an extension, until April 28, for all five as the investigation continues.

The three men held without charges were identified as Khamzat Bakhayev, Tamerlan Eskerkhanov, and Shagit Gubashev.

Reports by the official Tass and Sputnik news agencies shed little light on a possible motive for the Feb. 27 slaying of Nemtsov, 55, a former first deputy prime minister once seen as a possible president of Russia before the rise of Vladimir Putin.

Dadayev and Gubashev were detained Saturday in Ingushetia, Ingushetia Security Council chief Albert Barakhayev told Tass. Interfax news agency quoted an unidentified Chechen security officer as saying that another suspect blew himself up with a hand grenade as police moved in to arrest him in Grozny, the Chechen capital.