U.S. Secretary of State Hillary Rodham Clinton on Sunday acknowledged deep differences with Russia over how to handle the crisis in Syria, saying she would continue to try to convince Moscow to back increased international pressure on Syrian President Bashar Assad even if such a step is unlikely.

A day after Russia soundly rejected her call for UN sanctions to be imposed on Syria if Assad refuses to stop fighting and relinquish power, Clinton said she was "realistic" in her approach. She said that if the Russians refused to go along the United States and its friends would boost their support for the Syrian opposition.

"The United States disagrees with the approach on Syria," she told reporters at a news conference at the end of the annual Asia Pacific Economic Cooperation forum summit where she was filling in for President Barack Obama. "We have to bring more pressure to bear on the Assad regime to end the bloodshed and begin a political, democratic transition."

The Obama administration has been hoping to jack up pressure on Assad at the upcoming United Nations General Assembly session and potentially introduce a new UN Security Council resolution that would include sanctions. Russia and China have blocked three previous similar resolutions because they could lead to sanctions.

In discussions with Russian President Vladimir Putin and Foreign Minister Sergey Lavrov, Clinton said she had underscored the resolution "will only be effective if it includes consequences for non-compliance."

"There is no point in passing a resolution with no teeth because we have seen time and time again that Assad will ignore it and keep attacking his own people," she said. But, she allowed that convincing the Russians would be a tough, if not impossible sell.

"We have to be realistic," she said. "We haven't seen eye-to-eye with Russia on Syria." "That may continue, and if it does continue, then we will work with like-minded states to support the Syrian opposition to hasten the day when Assad falls and to help prepare Syria for a democratic future and help it get back on its feet again," she said.

After meeting Clinton on Saturday, Lavrov said bluntly Russia opposes penalties against the Assad government, in addition to new ones against Iran over its nuclear program, in part because they harm Russian commercial interests.