Bomb blasts in two cities in south-east Turkey killed nine civilians and wounded dozens on Wednesday, security sources said, and blamed the Kurdistan Workers Party (PKK) for the coordinated attacks targeting police.
A PKK commander had warned at the weekend of fresh attacks, saying police "will not be able to live as comfortably as they did in the past in cities."
Earlier in the day, four soldiers were killed and nine wounded when militants opened fire with rockets and long-range weapons from across the Iraqi border. Security sources also blamed that attack, in Sirnak province, on the PKK.
Turkey frequently launches air attacks against PKK targets in the mountainous regions of northern Iraq near the shared border, where the PKK leadership has camps.
A ceasefire between Turkey and the autonomy-seeking PKK fell apart last year, triggering some of the worst violence in decades in Turkey's mainly Kurdish south-east.
Four civilians were killed when roadside explosives were detonated by remote control near a hospital in the town of Kiziltepe in Mardin province, near the Syrian border, in an attack that targeted a bus carrying police, the sources said.
About 30 civilians and 10 police officers were wounded.
In the region's largest city, Diyarbakir, five civilians were killed in a car bomb attack apparently targeting police, the sources said, adding that 12 people were wounded in that attack, including five police officers.
A PKK commander, Cemil Bayik, said "a new style of war has been developed" in an interview published on Sunday by the Firat news agency, which is close to the group.
"The war will from now on be conducted everywhere without distinguishing between mountains, valleys and cities," Bayik said.
The United States strongly condemned the latest attacks. "We are in close touch with Turkish authorities and reaffirm our commitment to work together with Turkey to confront the scourge of terrorism," White House National Security Council spokesman Ned Price said in a statement.
Turkey is still dealing with the aftermath of a failed coup attempt on July 15 that killed more than 240 people and wounded 2,200.
More than 60,000 people, including many in the military and police, have been detained, suspended or placed under investigation since the coup attempt, in which rogue soldiers commandeered tanks and warplanes in an effort to take power by force.
The PKK, designated as a terrorist organisation by Turkey, the European Union and the United States, took up arms against the Turkish state in 1984 and over 40,000 people, mainly Kurds, have died in the violence.