"Not so long ago, information emerged that third countries have been illegally using regions of Afghanistan not under Kabul's control to train rebels to fight against the Syrian regime, including by training them in the use of deadly chemical substances," Russian Foreign Minister Sergei Lavrov told reporters.
"According to our information, the infamous Al-Nusra Front is planning to illegally deliver to Iraq poisonous agents and corresponding specialists in order to organise acts of terror on the territory of Iraq."
The Al-Nusra Front is an Islamist rebel group fighting in Syria suspected of links to Al-Qaeda.
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Lavrov did not spell out where or when Russia received such reports or what countries were allegedly training the Syrian rebels in Afghanistan.
Moscow accuses the rebels of staging an August 21 chemical attack near Damascus that Washington blames on Syrian President Bashar al-Assad's regime and believes killed more than 1,400 people.
Lavrov called on regional governments that oppose Assad to make sure that elements of the armed opposition also abide by the terms of a Russian-US Syrian chemical weapons destruction plan that began being implemented this month.
Relations between Russia and a number of Arab states opposing the Assad regime have sharply deteriorated during the Syria crisis, most notably with Saudi Arabia which has a history of difficult ties with Moscow.