Russian President Vladimir Putin said on Thursday that it was not Russia's job to remove Iran from Syria.
Speaking at the Russian resort city of Sochi, Putin said that it was important to "ensure a policy of non-intervention in Syria's affairs".
Putin added that ISIS had recently kidnapped 700 people in an attack on a refugee camp in eastern Syria and claimed that the organization was gaining strength in areas that were dominated by American forces.
Putin's remarks seemingly pose a challenge to Israel, which fears Iran establishing itself on its border with Syria.
Israel has expressed concern over Iran's growing influence in Syria, while the US has been pressing for Iran to withdraw its fighters from Syria.
Israeli officials have made clear that Israel will not accept any Iranian military entrenchment in Syria. Prime Minister Binyamin Netanyahu and Russian President Vladimir Putin have held several meetings to discuss the issue.
On Tuesday, NBC News reported that the Trump administration is developing a new strategy for the war in Syria that would focus more heavily on pushing Iran's military and its proxy forces out of the country.
The new strategy would not involve the US military directly targeting and killing Iranian soldiers or Iran's proxies, however, since that would violate the current US authorization for using force in Syria. The US military does have the right of self-defense under the authorization and could strike the Iranian military if it felt threatened.
The plan would emphasize political and diplomatic efforts to force Iran out of Syria by squeezing it financially, according to NBC News. It would withhold reconstruction aid from areas where Iranian and Russian forces are present, according to three people familiar with the plan. The US would also impose sanctions on Russian and Iranian companies working on reconstruction in Syria.