OTTAWA -- President Barack Obama spoke Wednesday with his Turkish counterpart Recep Tayyip Erdoğan to express sorrow following Tuesday's terror attack, White House Press Secretary Josh Earnest said.
"The President placed that phone call to express his deep condolences on behalf of the American people. In the context of that call, he will offer any support that the Turks can benefit from as they conduct this investigation and take steps to further strengthen their security," Earnest told reporters aboard Air Force One as Obama flew to Canada for a day of meetings.
Earnest said the attack will likely be discussed at next week's NATO summit in Poland as well. Turkey is a NATO member, which means the U.S. is treaty-bound to protect the country.
Earnest said Wednesday that he didn't have any update on how and when U.S. assistance in Turkey would be utilized.
Many officials believe that ISIS, also known as ISIL, is behind Tuesday's attack on Istanbul's Ataturk Airport, which killed more than 40 people, despite no claims of responsibility by the organization.
Earnest said the U.S. continues to make progress against ISIS in Iraq and Syria, but that the White House "continues to be concerned by the ability ISIL has to carry out terror attacks."
"We have made great progress and the Turks have made important progress in shutting off that border," Earnest said, referring to the boundary between Syria and Turkey through which many ISIS fighters have transited. "But there's more work to be done."
Earnest said the U.S. stood prepared to share any useful information about the investigation with Turkish authorities but didn't yet have details about the work of American intelligence agencies looking into the attack.
Obama last spoke with Erdoğan two weeks ago, when the Turkish leader phoned Washington to express his condolences following the Orlando terror attack.
The pair have a complicated relationship: Obama has pressed Erdoğan to take more steps to combat ISIS in his country, including better tracking the foreign fighters moving through the country to and from Syria. He's also pressed Erdoğan to enact Democratic reforms even as the Turkish leader seeks to consolidate power.
The attack is likely to arise in discussions in Ottawa Wednesday, where Obama will meet both separately and together with Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto.