President Barack Obama is chairing a U.N. gathering of world leaders to discuss countering terrorism, a day after he and the leaders of Russia, China and Iran addressed the General Assembly on its 70th anniversary.

At Tuesday's meeting, the United States is rallying support for the fight against groups like the Islamic State, which is attracting foreign fighters who could return to their home countries to launch attacks.

Russia on Wednesday will chair its own meeting on countering extremism as this month's U.N. Security Council president.

Both countries laid out competing visions Monday on Syria's conflict.

Also set for Tuesday are high-level meetings on the humanitarian consequences of the war in Syria and the wider refugee and migrant crisis that is the largest since the upheaval of World War II.