The Kommersant, a Russian daily newspaper, said in a report on Monday that police had detained the three men on suspicion of carrying out the murder of Andrei Kozlov, the first deputy chairman of Russia's central bank.
The report also said that the police have narrowed their search for those who ordered the contract killing.
"In the course of our investigation ... We have established those connected to organising and carrying out this crime," the general prosecutor's office said in a statement printed by Kommersant, on Monday.
The newspaper, citing sources close to the investigation, said that police were focusing on a number of banks which had come under the threat of losing their licenses about two months before Kozlov was shot dead on September 13.
Kozlov's murder is widely believed to be connected to his campaign against money-laundering and criminality in the banking sector.
The suspects, Alexei Polovinkin, Maxim Proglyad and Alexander Belokopytov, were detained last week and are cooperating with the investigation, Kommersant newspaper said in the report.
Olena Titorchuk, spokeswomen for the Ukrainian interior ministry, said the department had no information on the Ukrainians being detained.
Kozlov, who had been responsible for banking supervision, had withdrawn the licenses of dozens of banks and had overseen an ambitious scheme to reduce criminality and money laundering in Russia.
According to Russian media, the Russian central bank has shut down 90 credit institutions since 1994.