"And the fault, in the grand scheme of things, lies with those who fund and arm these opposition groups,” Foreign Minister Sergei Lavrov said in the southern Russian city of Rostov-on-Don.
Lavrov said the situation demanded "the prompt intervention of those with influence over the opposition.”
Nineteen armed Islamist groups in Syria said in a joint statement Saturday that participating in the Geneva 2 talks aimed at ending the Syrian civil war would be "treason” and attendees "would have to answer for it before our courts.”
The UN-backed conference, tentatively set for November 23, has been lobbied for by Russia and the United States, which took responsibility for bringing, respectively, the Syrian government and the opposition to the negotiation table.
However, many opposition groups have already said they will not attend the Geneva talks, and Syrian President Bashar Assad has also implied that the government’s participation is not guaranteed.
Lavrov did not name any rebels’ sponsors in his diatribe. Syrian Islamists are believed to enjoy broad support from Sunni Arab nations, including Saudi Arabia and Qatar.
Lavrov also criticized previous threats against countries seeking a political solution to the crisis, including Russia.
Three Russian diplomats sustained minor injuries during last month’s shelling of an area around the Russian embassy in Damascus.