WASHINGTON, Jan. 4 (Xinhua) -- U.S. President Barack Obama on Tuesday expressed his condolences for the victims in recent attacks in Turkey in a telephone call with his Turkish counterpart Recep Tayyip Erdogan, the White House said.

The extremist group Islamic State (IS) has claimed responsibility for the New Year attack against a nightclub in Istanbul that killed at least 39 people. The Kurdistan Freedom Hawks (TAK), a militant group linked to the Kurdistan Workers' Party, has claimed responsibility for the Dec. 17 attack against off-duty Turkish security personnel in Kayseri.

Obama and Erdogan agreed that Turkey and the United States must continue to stand united in order to defeat terrorism, the White House said in a statement.

Obama welcomed Turkey's ongoing efforts to work with regional actors to facilitate a nationwide cease-fire in Syria and a return to political negotiations between the Syrian government and the opposition.

Turkey and Russia have agreed on a cease-fire plan for all of Syria that aims to end nearly six years of war and lead to peace talks between the government and the rebels.

In the telephone talk, Obama and Erdogan noted recent progress in the U.S.-led international coalition's campaign against IS in Iraq and Syria, and agreed on the need to continue and deepen coordination between the United States and Turkey, according to the statement.

The two leaders also discussed the Cyprus issue and expressed hope that upcoming diplomatic engagements will result in an agreement to reunify the island as a bizonal and bicommunal federation.