The rebel-held section of Aleppo has been under intense air strikes by government forces and allied Russia since September when a U.S. -Russian-brokered truce collapsed in Syria.
U.S. Secretary of State John Kerry led the renewed talks, joined by a familiar cast that included Russian Foreign Minister Sergey Lavrov and the top envoys from Saudi Arabia, Iran, Turkey, Qatar, Egypt and Jordan.
The 5 1/2-year conflict, which has killed more than 300,000 people and displaced millions, is at increasing risk of morphing into a proxy war between Russian Federation, the US and regional powers. "There's no other option", Assad said.
The ministers go into the Lausanne meeting with low expectations, diplomats said.
He also said a victory in Aleppo would be "a very important springboard" to pushing "terrorists" back to Turkey. "This is the importance of Aleppo now". He estimated there were around 275,000 people in the besieged, eastern Aleppo.
The meeting comes as President Vladimir Putin gave signals Russian Federation is gearing up for a full-on war.
Pressure is rising for a halt to a ferocious, three-week-old Syrian regime offensive to capture the opposition-held eastern zone of the city of Aleppo.
Washington earlier this month pulled the plug on talks with Moscow on ways to revive a short-lived ceasefire that unravelled in September.
Lieutenant General Sergei Rudskoi of the Russian military's General Staff this week insisted no civilians in Aleppo had been targeted by Russian planes. "I would just say that we're working to get this multilateral effort and approach to Syria up and running", US State Department spokesman Mark Toner told reporters in Washington.
One scenario to be discussed involves direct USA military action in Syria, including airstrikes on Syrian military, radar and anti-aircraft bases, as well as arms depots, Reuters reports citing high-ranking U.S. officials who spoke on condition of anonymity.
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According to The Aleppo Media Centre, a group of opposition activists in the city, the overnight air strikes killed and wounded a number of people, with some buried under the debris. "This will be a turning-point - it will immediately resolve all the problems with the terrorists".
"They don't care whatever we say about humanitarian law".
He said Aleppo is effectively no longer Syria's industrial capital but taking back the city would provide important political and strategic gains for his regime.
President Barack Obama planned to convene his National Security Council for a highly anticipated meeting about Syria on Friday.
One of the options they are set to discuss is providing allies with more sophisticated weapons, except shoulder-fired anti-aircraft missiles which it's feared could be used against Western airlines. The Obama administration has refused to supply Manpads for fear they would end up in the hands of Islamic State or other jihadists.
"The Russians are seeking to maximise their advantage before (President Barack) Obama's successor - probably (Hillary) Clinton - steps in with a likely firmer approach to Syria", said Karim Bitar, a researcher at the Institute for global and Strategic Affairs think tank in Paris.
President Bashar Al Assad of Syria intends to capture all of Aleppo at all costs and use the city as a "springboard" from which to liberate other areas of the country.
With an nearly total siege imposed since early September, Russia's hope is that the opposition will be forced to surrender eventually, he said.
Earlier this week, Russian Federation announced plans to build a permanent naval base in the Syrian port of Tartus.