Baghdad, Iraq (CNN) -- Robbers stole $5.5 million from a southern Iraqi state bank after giving guards tea laced with a sleeping drug, the Interior Ministry said on Saturday.
No shots were fired during the incident Friday at a bank near Najaf, the Interior Ministry said. The money is the equivalent of 6.5 billion Iraqi dinars.
In recent months, there has been a spike of similar incidents and authorities believe that insurgents were behind them to fund their military operations
Earlier this week, 15 people died in southwestern Baghdad after a brazen series of jewelry store heists on Tuesday in which bandits made off with gold and money.
In this latest incident, robbers had an associate among the bank's guard force give drugged tea to the guards, officials said.
After the guards passed out, the robbers entered the bank and made off with the money.
Two people were arrested, but police were not able to recover any of the money. The Interior Ministry said it appears the two are poor people trying to make money and are not part of a terrorist organization.
Members of the bank's guard force are being investigated, the Interior Ministry said.
CNN's Frederik Pleitgen and Mohammed Tawfeeq contributed to this report.