The leaders of Turkey, Russia and Iran meet on Monday to try to secure a lasting truce in northwest Syria following attacks by the government that risk deepening regional turmoil and pushing a new wave of migrants towards Turkey.

The summit in Ankara, bringing together countries whose Syrian allies are combatants in a ruinous eight-year-old war, will focus on the Idlib region, the last remaining territory held by opposition fighters seeking to overthrow President Bashar al-Assad.

Russian President Vladimir Putin and Iran’s Hassan Rouhani have backed Assad against the opposition. Turkish President Tayyip Erdogan, along with the United States, European and Arab allies, has supported different oppositions factions in the conflict.

Assad’s forces, aided by Russian air power, have regained control of most lands lost in the war. In recent months, Assad’s forces have attacked Idlib, where Syrian and foreign radical fighters hold sway alongside other more moderate factions.