The State Department on Monday announced it received credible threats of "potential terrorist activity" targeting U.S.-branded hotels in Adana, Turkey, warning Americans in the southern city to "exercise extreme caution."

The warning continued, "U.S. citizens should avoid travel to southeastern Turkey and carefully consider the risks of travel to and throughout the country."

Turkey has blamed the Kurdistan Workers' Party, or PKK, for a string of deadly attacks, many of them in the southeastern part of the country. In addition, attackers with guns and bombs killed more than 40 people at Istanbul's Ataturk airport in June -- a rampage blamed on the Islamic State.

Fighting between the PKK and Turkey's security forces resumed last year after a fragile peace process collapsed. Since then, more than 600 Turkish security personnel and thousands of PKK militants have been killed, according to Anadolu. Human rights groups say hundreds of civilians have also died in the violence.

Tens of thousands of people have died overall since the PKK -- considered a terror organization by Turkey and its allies -- took up arms in 1984.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.