Russian Foreign Minister Sergei Lavrov will meet U.S. Secretary of State John Kerry in Geneva in fresh attempts to broker a ceasefire in Syria, Russia's Foreign Ministry has announced.

The U.S. State Department did not confirm that the pair would meet, but said but that Lavrov and Kerry held a 45-minute phone conversation on Wednesday.

“These issues are complex and we have not been able to reach a clear understanding between us on the way forward.” said State Department spokesperson Mark Toner. “The United States' patience isn’t finite,” he said.

U.S. President Barack Obama reportedly gave Russian President Vladimir Putin a “final proposal” for a ceasefire deal and coordinated anti-terror cooperation during the G20 summit in China last week, The Washington Post reported Thursday.

The proposal includes a country-wide ceasefire and plans for humanitarian provision. The plans also allegedly see Russia bring Syrian forces under its control, before beginning a joint air campaign with the United States.

Disagreements center on Aleppo and the Al-Nusra Front, one unnamed U.S. official told The Guardian newspaper. The Kremlin has designated the group as terrorist, while the United States identifies Al-Nusra fighters as “moderate rebels.”

Further U.S.-Russia talks may be further complicated by new U.S. sanctions against Russia over its continuing role in the Ukraine conflict. Lavrov told Kerry on Wednesday that “normal cooperation is impossible without basic decency,” Russia’s Foreign Ministry said in a statement Wednesday.

The Syrian High Negotiating Committee (HNC) met in London on Wednesday, presenting new plans for a peaceful political transition away from the Assad regime. The document, the most comprehensive ever drawn up by the HNC, advocates for a transitional governing body to run Syria for 18 months, leading up to UN-sponsored elections.

The U.S. and its Western allies insist that Syrian President Bashar Assad must be removed from power, accusing his government of indiscriminate use of barrel bombs, incendiary and chemical weapons.

Russia however, have consistently claimed that Assad is Syria’s only legitimate ruler.

The Islamic State and the Al-Nusra Front are a terrorist organization banned in Russia.

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Syrian Ceasefire in the Balance as Kerry and Lavrov Prepare for Fresh Talks