The Kurdistan Freedom Hawks (TAK) said in a statement emailed to websites close to the terrorists that they had fired on the vehicle carrying military personnel close to Foça, a small resort town on the western Aegean coast which is home to a naval base.
TAK has claimed responsibility for some past attacks outside the PKK's regular area of operation in the mainly Kurdish southeast, such as a car bomb in Ankara in September 2011 that killed three people.
Turkish Prime Minister Recep Tayyip Erdoğan said Thursday's attack, which occurred at a time of intensified clashes between the army and the PKK, was an example of "widening terrorism".
Turkish media reported on Sunday that the driver of the bus had died of his injuries in hospital, bringing the death toll to two.
The PKK has fought for autonomy for Turkey's mainly Kurdish southeast since 1984, in a conflict which has cost more than 40,000 lives, most of them Kurdish. Turkey, the United States and the European Union list the PKK as a terrorist organisation.
In the statement TAK warned that "its warriors were willing to play their part all over Turkey".
In 2010 TAK claimed responsibility for a bomb attack on a military bus that killed five people, and a suicide bomb attack that wounded 32 people in İstanbul.
Increased PKK violence is a problem for Erdoğan as he tries to limit the effect at home of the conflict in Syria, where the PKK exerts growing authority in Kurdish areas and is receiving arms from Syrian forces, Ankara has said.
Turkish authorities in the southeast province of Hakkari announced on Saturday that the armed forces had completed an almost three-week operation against PKK positions around the region of Şemdinli, the scene of some of the fiercest fighting of recent years.
Erdoğan said the PKK had suffered heavy losses and left the area.