The United States is prepared to work with any nation, including Russia and Iran, to resolve the conflict in Syria, US President Barack Obama said Monday.

"While military power is necessary, it is not sufficient to resolve the situation in Syria," Obama said at the general debate of the United Nations General Assembly (UNGA). "Lasting stability can only take hold when the people of Syria forge an agreement to live together peacefully."

Accusing Syrian President Bashar al-Assad of killing tens of thousands of his own people, Obama said that the world must recognize that "there cannot be a return to the prewar status quo" in Syria.

Obama's remarks came amid US concerns about Russia's recent military buildup in Syria and after the announcement on Sunday of an understanding among Iran, Iraq and Syria to share intelligence about the extremist group Islamic State (IS).

"There is no room for accommodating an apocalyptic cult like ISIL and the United States makes no apology for using our military as part of a broad coalition to go after them," Obama said, using an alternate acronym for the extremist group.

Russian President Vladimir Putin and Iranian President Hassan Rouhani are also expected to talk about the Syrian crisis as they address the UNGA on Monday. Obama and Putin are scheduled to meet later on the day.

In an interview with CBS that aired on Sunday, Putin reiterated his support for al-Assad, saying that there is no other solution to the Syrian crisis than strengthening the effective government structures and rendering them help in fighting terrorism.

"We are considering intensifying our work with both President Assad and with our partners in other countries," Putin said.