ROSTOCK, Germany (Reuters) - Europe will not be blackmailed by Turkey in talks on visa liberalization, German Vice Chancellor Sigmar Gabriel said on Monday as relations with Ankara are strained in the aftermath of a failed coup.

Turkish Foreign Minister Mevlut Cavusoglu said over the weekend that Ankara would back out of its agreement with the EU to stem the flow of migrants if the bloc does not deliver the promised visa-free travel for Turks in return.

Visa-free access has been subject to delays due to a dispute over Turkish anti-terrorism legislation and the post-coup crackdown. Berlin urged Turkey to show proportionality in its pursuit of those behind the coup, comments that angered Ankara.

"It is up to Turkey if there is or there isn't visa liberalization," Gabriel said. "Germany and Europe should under no circumstances be blackmailed."

Gabriel applauded a decision to prevent Turkish President Tayyip Erdogan from addressing via video-link a rally in Cologne on Sunday. The ban prompted the Turkish Foreign Ministry to summon the German charges d'affaires.

Foreign Minister Frank-Walter Steinmeier said it remained up to Turkey to fulfill the conditions required for visa liberalization.

"Turkey still has work to finish off here. Whether they do this under the current conditions we will have to wait and see," Steinmeier told reporters.

(Reporting by Holger Hansen and Reuters TV; Writing by Joseph Nasr and Caroline Copley; Editing by Paul Carrel and Robin Pomeroy)