A senior U.S. official from the Obama administration said on Monday that there was no scenario where the embattled Syrian President Bashar al-Assad could hold onto his power as the United States was pushing hard for a UN resolution on the Arab state.

"Frankly, increasingly it's clear that there is not a scenario where he can hold onto power," said White House Deputy National Security Advisor for Strategic Communications Ben Rhodes in a discussion at the Washington-based Center for American Progress.

But he admitted that the United States had run into challenges at the UN Security Council "where there hasn't been a strong resolution we like" due to the oppositions from members in the Security Council.

Rhodes believed that the sanctions imposed by the Untied States, EU and other countries have had a direct impact on Syria's economy and the Assad government's ability to finance the crackdown.

He vowed that Washington would continue to rally countries around the world for broader sanctions on Syria and continue its unilateral steps to address violence and political transition in the country.

Rhodes' comment came at a time when the United States was pushing hard for a strong UN resolution on Syria. On Monday, U.S. Secretary of State Hillary Clinton, who would attend a Security Council meeting on Syria slated for Tuesday, called on the Council to act and send a clear message of support to the Syrian people.

Russia's Deputy Foreign Minister Gennady Gatilov said on Monday that his country would not back the latest Western-Arab draft resolution on Syria, describing the new draft resolution as " unacceptable" as a similar version last October.

Damascus has rejected a new plan suggested last week by the Arab League which asked President al-Assad to delegate power to his first vice president and envisioned the formation of a national unity government within two months.

The UN says at least 5,400 people have been killed in the unrest that began in March, while the Syrian government acknowledges more than 2,000 army and security personnel are among those killed in the violence.