"We call for an immediate ceasefire in the southeast and strongly condemn all kinds of terrorism," Mogherini told a joint press conference with Turkish ministers in Ankara.
"We are ready to contribute with regards to the Kurdish peace process. We have an imminent interest on that because it can affect the security in the region, and in the broader sense, the EU," added European Union Enlargement Commissioner Johannes Hahn.
After a more than two-year ceasefire, fighting resumed last summer between Turkish security forces and the PKK, dashing hopes of ending a conflict that has killed more than 40,000 people since 1984.
But Turkey's EU Affairs Minister Volkan Bozkir vowed no let-up in the campaign against the PKK, which has since staged a string of attacks against security forces.
"As a sovereign state, Turkey will continue its struggle against all terrorist organisations, including the PKK, which are threatening its national security," he said, according to AFP.
"In doing so, we try to protect the rights of our citizens."
Vowing to flush out the PKK from Turkey's urban centers, the authorities have in recent weeks enforced curfews in three locations in the southeast to back up military operations that activists say have killed dozens of civilians.
Prosecutors have launched a vast investigation into over 1,200 academics for engaging in "terrorist propaganda" by signing a petition urging Ankara to halt "its deliberate massacres" in the Kurdish-majority region.