"Russia will be grateful to all of our friends for any information about the criminals who killed our citizens in Iraq," Putin said here during a meeting with visiting Saudi Arabian Prince Salman bin Abdul-Aziz Al Saud, according to the Kremlin.

Director of the Federal Security Service Nikolai Patrushev said he had received instructions from the president to track down the terrorists responsible for the killings.

Russian special forces will make every effort to bring the murderers to justice, Patrushev told Moscow press.

"We should be working so that not a single terrorist responsible for the crime would escape responsibility," Patrushev said, adding that "we will go on working no matter how much time and effort will be needed."

Also on Wednesday, Russia's upper house, the State Duma, passed a statement on Wednesday, saying that the occupying countries are to be blamed for the killings.

The statement asked "the Iraqi authorities and the occupying countries" to conduct "a thorough and profound investigation of the murder of the Russian citizens in Iraq" and insisted that all necessary measures should be taken to arrest and punish the criminals.

The Russian Foreign Ministry confirmed the deaths of the four diplomats, kidnapped on June 3 in Baghdad, on Monday, a day after the Mujahedeen Shura Council, an umbrella organization grouping several insurgent groups in Iraq including the al-Qaida terror network, said in an Internet statement that it had carried out the killings.