The leaders of Turkey, Russia and Iran on Monday agreed at a meeting in Ankara to try to ease tension in north-west Syria's Idlib region.
But disagreements between the countries appeared to linger, especially over the threat from ISIS.
The summit of the three countries, all of whom have allies fighting in Syria's eight-year war, aimed to find a lasting truce there.
Recent attacks by Syrian government forces risk worsening the regional turmoil and pushing a new wave of migrants towards Turkey.
"We are in a period when we need to take more responsibility for peace in Syria, when we need to carry more weight," Turkish President Recep Tayyip Erdogan said.
Mr Erdogan said all three leaders agreed that a political solution was necessary to end the crisis in Syria.
Russian President Vladimir Putin and Iranian leader Hassan Rouhani have supported Syrian President Bashar Al Assad against the rebels.
Mr Erdogan and the US have supported different rebel factions.
On Monday, the three leaders said they were alarmed about the risk of further deterioration of the humanitarian situation in and around Idlib.
They said they had agreed to take concrete steps to stop breaches of previously negotiated agreements.
Disagreements appeared to persist, however, in particular over the threat from ISIS, which Mr Erdogan dismissed while Mr Putin expressed concern.
"Of course we are worried by the situation in north-east of Syria, where sleeping cells of ISIS are emerging," Mr Putin said, minutes after Mr Erdogan claimed the only threat there was from Kurdish militant groups.
Standing alongside the other two leaders, Mr Rouhani said the attacks on two major Saudi oil plants were a reciprocal measure by "Yemeni people" to assaults on their country.
"Yemeni people are exercising their legitimate right of defence," he said.
"The attacks were a reciprocal response to aggression against Yemen for years."
Mr Erdogan focused on a planned "safe zone" with Russia and Iran in northern Syria, which he said could host up to 3 million refugees currently living in Turkey if it were extended from the Turkish border to Deir Ezzor and Raqqa.
Neither Mr Putin nor Mr Rouhani commented on the Turkish plans and the joint statement did not refer to them.
Mr Rouhani said before the talks that diplomacy was the only solution to the crisis and called on the US to withdraw its troops from north-eastern Syria immediately.
Against the advice of his top aides and commanders, US President Donald Trump said last year he would withdraw US troops from Syria.
The move was welcomed by Turkey and Iran, but has yet to be fully implemented.
Turkish and US forces launched joint land patrols in northern Syria as part of a safe zone at the east of Euphrates River more than a week ago.
"Diplomacy and not confrontation can secure peace in Syria," Mr Rouhani said.
Their joint statement said their talks focused on Idlib, the last remaining territory held by rebels seeking to overthrow Mr Al Assad.
Syrian troops on Sunday shelled the south of Idlib in the area where a truce halted the fierce army offensive two weeks ago.
Turkey, which has a 911-kilometre border with Syria along its southern frontier, has 12 military observation posts in the region, under a deal with Moscow and Tehran in 2017.
Mr Erdogan warned that Turkey would retaliate against any Syrian government attack on Turkish posts.
He and Mr Putin, who agreed last month to try to "normalise" the situation in Idlib after Syrian troops encircled rebels and a Turkish post in the region, repeated the need to root out militant groups.
"Russia, on its part, plans to support the Syrian army while it carries out local operations aimed at removing the terrorist threat where it emerges," Mr Putin said.