ISTANBUL - The White House says President Barack Obama has offered his condolences to Turkey's leader over a pair of deadly attacks, including at a nightclub on New Year's Eve.

Obama and Turkish President Recep Tayyip Erdogan also agreed during their telephone conversation Tuesday that their countries must "stand united" to defeat terrorism.

The Islamic State group has claimed responsibility for the Dec. 31 shooting at Istanbul's Reina nightclub that killed 39 revelers.

Obama also expressed sorrow over a Dec. 17 attack on off-duty Turkish soldiers in the central province of Kayseri that killed 13 troops. A wing of the outlawed Kurdistan Workers' Party has said it was responsible.

The White House said Obama also welcomed Turkey's efforts to help implement a nationwide cease-fire in Syria as well as the resumption of political talks between the Syrian government and the opposition.