Russia is offering a $10m (£5.4m) reward for information leading to the capture of the militants who killed four Russian diplomats in Iraq.
The Russians were seized on 3 June
A group linked to al-Qaeda released a video on Monday showing two of the captives being killed.
Russian President Vladimir Putin has ordered special services to "find and destroy" the killers of the hostages, who were abducted in early June.
The reward offer has been widely publicised on Arab television channels.
'Time and effort'
"In return for information leading to a result, Russia's National Anti-terrorist Committee will pay a reward of $10m," said Nikolai Patrushev, head of Russia's security service, in televised comments.
He promised earlier this week to carry out Mr Putin's order "however much time and effort it requires", Russia's Interfax news agency reported.
BOUNTIES FOR WANTED MEN
$25m - Offered by US for information on Osama Bin Laden (at large)
$25m - Offered by US for information on militant leader in Iraq Abu Musab al-Zarqawi (now dead)
$25m - Offered by US for information on Saddam Hussein (now on trial)
£10m - Offered by Russia for information on Chechen militant Shamil Basayev (at large)
$5m - Offered by US for information on former Bosnian Serb leaders Ratko Mladic and Radovan Karadzic (at large)
A Russian official said the country had received offers of help on the issue from "many overseas partners".
The Russian embassy employees were abducted when gunmen attacked their vehicle in the west Baghdad neighbourhood of Mansur on 3 June.
A fifth Russian citizen was killed during the kidnapping.
The video posted on the internet on Monday by the militant group, the Mujahideen Shura Council, showed one of the captives being beheaded and another being shot. The body of a third man was also shown.
Russia confirmed all the deaths the following day.