The report came less than a week before the Russian presidential election on Sunday, raising questions about the timing, in part because two suspects were arrested weeks ago. Mr. Putin, the dominant figure in Russian politics, is widely expected to return to the presidency, which he held for two terms before becoming prime minister in 2008.
The report by the government-controlled broadcaster, Channel One, said the two suspects were arrested in the Ukrainian city of Odessa after surviving an explosion in an apartment there on Jan. 4. A third man died in the blast, which occurred while the men were mixing chemicals for an explosive device, according to the report. The authorities said the Chechen militant leader Doku Umarov had sent the three men to the city, Channel One reported.
One suspect, Ilya Pyanzin, was arrested immediately after the explosion and the second, Adam Osmayev, a month later, according to the report.
“We were told to first go to Odessa and study how to prepare a bomb,” Mr. Pyanzin told the authorities in a recorded deposition. “In Moscow, we were to sabotage economic sites — and then assassinate Putin.”
Mr. Putin’s spokesman, Dmitri S. Peskov, confirmed on Monday that an assassination attempt had been in the works, as did a spokeswoman for the Ukrainian Security Service. A spokesman for Russia’s Federal Security Service, which took part in the investigation, declined to comment.
A spokesman for Channel One told the Ria Novosti news agency that Russian special services agents had contacted the channel about the investigation in early February and that the report on Monday had been prepared over the previous 10 days. The channel released what it said were preliminary details about the plot, including filmed depositions from the two suspects.
The police allowed a reporter for Channel One to interview Mr. Osmayev, who said: “The final goal was to go to Moscow and attempt to carry out an attack on Prime Minister Putin. There are combat mines, which are called armor-piercing mines. So it wouldn’t necessarily be a suicide bomber. The man who died, for instance, was ready to be a suicide bomber.”
Mr. Osmayev was arrested on Feb. 4 in a joint operation by Russian and Ukrainian agents, Marina Ostapenko, a spokeswoman for the Ukrainian Security Service, said in a telephone interview. One scene in the 10-minute Channel One report showed black-clad officers, wielding pistols and automatic weapons, charging into an Odessa apartment building and detaining Mr. Osmayev. He appears on camera bloodied and bruised, apparently from a scuffle during the arrest.
Mr. Osmayev, who was reported to have lived in London for years, said he and the other two men had studied the routes of Mr. Putin’s drivers in Moscow and were in the final stages of preparation. “The deadline was after the presidential election,” he said.
Channel One reported that Mr. Osmayev had revealed details of the plan, and those of a plot that Russia’s domestic intelligence agency foiled in 2007, in the hope of receiving leniency from prosecutors. He has also been implicated in an earlier plot to assassinate the leader of Chechnya, Ramzan A. Kadyrov.
A Russian security services official, who spoke to Channel One on the condition of anonymity, said investigators searching computer files found in the Odessa apartment had discovered video of several senior government officials’ routes through Moscow, among them Mr. Putin’s. The official said detonators and plastic explosives had been brought to Moscow earlier.
“It would have been a decent explosion — enough to overturn a truck,” the official said.
Russia’s president, Dmitri A. Medvedev, warned this month of possible terrorist threats from Russia’s volatile North Caucasus region, which includes Chechnya, before the election.
“The most important political event of the year is the election for president of the Russian Federation,” Mr. Medvedev said at a meeting with the officers from the Federal Security Service. “It is obvious that there could be different reactions to this event, and it is not out of the question that in the period of the campaign the criminal underground in the North Caucasus could become active.”
Mr. Umarov, the Chechen militant leader who has claimed responsibility for numerous attacks, including those on subway stations and at an airport in Moscow, called on his followers this month to refrain from attacks on civilians in light of a recent protest movement against Mr. Putin.
“The recent events show that the people of Russia support Putin,” Mr. Umarov said in a video posted on the Internet. “Thus, I order all groups carrying out special operations on the territory of Russia and make peaceful citizens to suffering.”