Obama, in a meeting with Turkish President Recep Tayyip Erdogan, vouched for the NATO ally's right to self-defence, and he pledged a solid US commitment "to Turkey's security and its sovereignty."
Yet he emphasized the need for Turkey and Russia to "de-escalate" their conflict and not get distracted from the campaign against IS and efforts to resolve Syria's long-running civil war.
Tensions between Turkey and Russia have erupted into diplomatic crisis since Turkey shot down a Russian jet it accused of violating its airspace less than two weeks ago.
Russian President Vladimir Putin has claimed Turkey shot the plane down to protect oil he says Turkey is illegally importing from IS, a charge Turkey vehemently denies.
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Turkey has insisted it won't apologise for the shoot-down, which also led Russia to slap a package of new sanctions against Russian products.
After IS claimed responsibility for the Paris attacks and shooting down a Russian passenger jet in Egypt, Obama had sought to turn the outrage across Europe into newfound resolve for stepping up the fight against IS.
To that end, Obama has been working to persuade Russia to focus its airstrikes in Syria against IS, instead of US-backed rebels fighting Syrian President Bashar Assad.
Further muddying the diplomatic picture, Moscow has steadfastly supported Assad while the US and Turkey insist he must leave power as part of a political solution to Syria's civil war.
He also praised Turkey for generously accepting refugees fleeing violence in Syria, and credited Turkey with strengthening security along its border.
Turkey, too, hopes to avoid tensions with Russia, Erdogan told reporters as he and Obama finished their roughly hour-long meeting. Waxing optimistic about a new diplomatic effort in Vienna aimed at a ceasefire in Syria's civil war, Erdogan said he hoped it would result in "sigh of relief for the entire region."