His comments come as the United States, Russia and other members of the United Nations Security Council continue to hammer out the details of a Syrian disarmament plan at U.N. headquarters in New York.
That opposition, combined with continued shipments of Russian military hardware to Assad's forces, has been part of Moscow's strategy to bolster its main Mideast ally.
Council members have reportedly agreed to broad terms on a U.N. resolution forcing embattled Syrian President Bashar Assad to hand over his chemical arsenal to international control.
The five permanent members of the council, led by the United States and Russia, will meet again Friday to coordinate a Syrian peace conference in Geneva, according to recent reports.
Assad has submitted his assessment of the country's chemical weapons stockpiles to United Nations investigators, clearing the first hurdle toward an eventual disarmament deal.
Officials from the Organization for the Prohibition of Chemical Weapons (OPCW) received the stockpile disclosures from Damascus in late September, according to an organization statement.
A final disarmament resolution could be ready for a full council vote within days, reports state.
The resolution, proposed by Russia last month, put the brakes on White House plans to begin targeted strikes against Assad's forces inside Syria.
The attacks would have been in retaliation for chemical weapons strikes by Assad's troops against anti-government rebels in the country.
While the proposed U.N. resolution will allow foreign military support to aid the Syrian weapon handover, the deal does not allow military action to force Assad to comply with the disarmament mandates.
If Assad fails to meet the terms of the resolution, council members will be forced to approve a second resolution authorizing military intervention in Syria.
Many on Capitol Hill have argued that without the threat of military force, a disarmament deal would be destined to fail.
Without that threat of U.S. force, "Syria's willingness to follow through is very much an open question," Tennessee Sen. Bob Corker, the top Republican on the Senate Foreign Relations Committee, said shortly after the Russian proposal was announced.
However, President Obama made clear the disarmament deal included serious "consequences" for the Assad regime if it failed to comply with U.N. weapons regulators.