Putin said Moscow would be grateful to all its friends for any information leading to those who killed the Russians.
Russia's Foreign Ministry on June 27 called on Iraqi authorities and coalition forces find those responsible for the crime and make sure they were brought to justice.
The four workers were seized in Baghdad on June 3. A fifth was killed during the kidnapping. A group linked to Al-Qaeda claimed responsibility.
The Duma, the lower house of the Russian parliament, on June 28 unanimously passed a declaration that said the killings had become possible because coalition forces were "losing control over the situation" in Iraq.
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