"It's been determined that (the explosion) was a bomb," a police officer in the town of Cesme said on Sunday.
Kurdistan Liberation Hawks (TAK), a militant wing of the banned Kurdistan Workers Party (PKK), has claimed responsibility for the bombing.
The group was quoted by the Europe-based Mezopotamya news agency as saying on Sunday that it would carry out more attacks.
"A person describing himself as an official from TAK telephoned Mezopotamya and said that they were responsible for the attack in Cesme today," the agency, believed to be close to the separatists, said.
Explosives were stashed into a soda bottle that was placed in a garbage can near a bank in downtown Cesme, a popular tourist destination, some 70km from the Aegean port city of Izmir, police said.
At least one victim was seriously wounded, he said.
Anatolia news agency said two foreign tourists - John Willoghby, 63, of Britain, and Aleksander Daniluk, 44, of Russia, were among the injured. Willoghby suffered a light flesh wound, while Daniluk was injured in his left arm, Anatolia reported.
Bomb experts were still investigating at the scene of the blast, and police have sealed off the area.
"A person describing himself as an official from TAK telephoned Mezopotamya and said that they were responsible for the attack in Cesme today"
Mezopotamya news agency
There were no claims of responsibility for the explosion, which happened at around 2.30pm (1230 GMT).
A Kurdish separatist group claimed responsibility in April for a bombing in Kusadasi, another Aegean Sea resort centre. One police officer died in that attack.
Rebels and far-left goups have also been behind bomb attacks in Turkey in the past.
Turkey's worst peacetime attack was in November 2003, when four bombings were carried out against Jewish and British targets. More than 60 people were killed and hundreds were wounded in the attacks.