Iraqi Prime Minister Nouri Maliki has launched an investigation into the deal, said his spokesman.
The purchase – said to include attack helicopters and missiles – was only signed off in October.
Iraq has been rebuilding its armed forces since the end of US-led combat operations against insurgents.
Announcing the cancellation of the purchase on Saturday, a spokesman for Prime Minister Nouri Maliki told AFP news agency that “when Maliki returned from his trip to Russia, he had some suspicions of corruption, so he decided to review the whole deal”.
“There is an investigation going on, on this,” he added.
The sale would have made Moscow – the main supplier of arms to Iraq under Saddam Hussein – the country’s second-biggest arms supplier after the US.
There has been no word from Russia about the cancellations.
In early October, Nouri Maliki said in a speech that he did not want Iraq to be “part of someone else’s (arms) monopoly.”
But he faced criticism from political opponents who questioned buying from Russia, when multiple deals with the US had been signed.
One Iraqi MP suggested that counterterrorism operations – the stated aim of the purchase – required improved intelligence, and not the 30 Mi-28 attack helicopters that were reported to be part of the deal.
The contracts were announced to some fanfare on 9 October after talks between the two countries’ prime ministers near Moscow.
At the time the deal was agreed, analysts suggested that while it was clear Iraq wanted to diversify its weapons purchases, buying from Russia would only encourage the sense in Washington that the US is somehow “losing Iraq”.
Nouri Maliki – who said he was seeking “quick contracts to fight terrorism” – warned even before he left that anything he signed might be scuttled by parliament.
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