Turkish authorities on Thursday detained 15 people in connection with a suicide bomb attack in the northwestern city of Bursa which wounded 13 people, Interior Minister Efkan Ala said.

The female attacker blew herself up near an Ottoman-era mosque in Bursa's historic district on Wednesday. None of the wounded was in serious condition.

Ala did not provide details on the suspects. Earlier, the state-run Anadolu Agency said 12 suspects were detained in Bursa, Istanbul and two other cities.

No group has claimed responsibility for the attack and authorities have refused to disclose details on the identity and possible affiliation of the attacker until the end of the investigation. The assailant was "aged about 25" and only fragments were left of her body, according to the country's health minister.

The attack occurred a day after the United States issued a new warning to its citizens about "credible indications" of terrorist threats against tourist areas in Turkey.

The country, which is facing growing blowback from the conflict in Syria and renewed conflict with Kurdish militants, has recently witnessed an increase of such attacks. In the past year, more than 200 people across Turkey have been killed in seven suicide bombings, including Wednesday's.

Kurdish militants, who have been fighting state security forces in a renewed conflict in the southeast, have claimed two such attacks recently.

Turkish authorities have blamed four of the attacks on the Islamic State group, which controls territory in neighboring Syria and Iraq. The extremist group is known to have cells in Turkey but never claimed responsibility for any of the suicide attacks on Turkish soil.