U.S. Secretary of State Hillary Clinton called Russia’s lack of cooperation in efforts to resolve the current political and humanitarian crises in Syria, despite Moscow’s influence with Syrian authorities, “troubling” and “frustrating.”

“It is a very troubling and frustrating situation because the Russians continue to say, oh, they're for humanitarian aid, but then they don't produce any plan that Assad will sign off on,” Clinton told members of the House Foreign Affairs Committee on Wednesday.

"We are doing everything we can think of to influence the Russians and the Chinese, particularly the Russians: they're the ones with the very deep, long-standing relationship with the Assad family, with Syria," she said.

Russia and China have twice vetoed U.N. Security Council resolutions on Syria that they believe could lead to a military operation against Syrian government forces as a repetition of “the Libyan scenario.”

Russia has also opposed calls to establish air corridors in Syria to provide humanitarian aid to civilian population suffering from the consequences of clashes between troops loyal to President Bashar al-Assad and opposition forces.

Clinton expressed hope that Russia would finally agree to cooperate with the international community as it could be key to resolving “a terrible crisis that demands the entire world's attention.”

"We know that if we can persuade them to work with us, at least on the humanitarian issue, they will have access to Assad that hardly anybody else does have, at least nobody in the West," she said.

Syria has been the scene of continuous anti-government protests for nearly a year. According to the United Nations, more than 7,500 people have died in the unrest.

Last week Clinton attended the “Friends of Syria” conference in Tunisia. The conference participants issued a declaration calling on Damascus to end violence immediately and to endorse the main opposition umbrella group, the Syrian National Council (SNC), as a "credible" voice of opposition.

Delegates from more than 70 countries also called on President Assad to allow humanitarian access and vowed to step up sanctions against the regime.

Russia and China refused to attend the meeting, sparking an angry reaction from the United States.