Turkey remains an EU membership candidate despite deep concerns over its rights and rule of law record preventing fresh accession talk.
At a tense press conference with two visiting Turkish ministers, Mogherini however warned that "concrete steps" were needed before there could be any progress on Ankara's long-stalled candidacy.
"Clearly Turkey is and stays a candidate country," Mogherini said after meeting Turkish Foreign Minister Mevlut Cavusoglu and EU Affairs Minister Omer Celik in Brussels.
Mogherini stressed the importance of their "frank and constructive" talks to resolving differences but said it would "be difficult at the moment to open new chapters" in the accession process.
"We have raised what is very important for us, which is not so much to hear during our dialogue, but to see concrete steps in the field of rule of law, human rights, democracy, media freedom."
Relations with Turkey, and especially between Berlin and Ankara, have hit rock bottom in recent months, stoking calls for Ankara's EU accession talks to be suspended outright.
Turkey began formal membership talks in 2005 after years of foot-dragging by some EU member states such as France who were wary of admitting such a large Muslim country.
But progress was slow and the negotiations came to a virtual halt last year as Turkish President Recep Tayyip Erdogan rounded up opponents in a massive crackdown after a failed coup.
In December, EU member states agreed that no new accession chapters would be opened until Ankara reversed course.
Cavusoglu and Celik were dismissive, recalling that the EU had promised to speed up the negotiations under a 2016 accord on controlling the flood of refugees pouring through Turkey into Greece and then onto northern Europe.
"Many countries say they do not like the idea of new chapters being opened but the core of relations with the EU revolve around accession," Celik said.
"The March migrant deal emphasised this," he said. "If there is a problem on the rule of law then the answer is to open the chapters to discuss it."
Cavusoglu said repeatedly that Turkey stood by agreements it signed while the coup crackdown was fully justified by the need to combat terrorism, a goal the European Union shared.
"We have not seen enough support from the EU" over the coup, he said, insisting: "Nobody can say there is no law in Turkey."
The Turkish ministers also rejected criticisms from rights group Amnesty International, whose chief met with Mogherini earlier Tuesday to urge the EU to "reset" relations and press Turkey to free detained activists.
EU Enlargement Commissioner Johannes Hahn, who also attended the meeting, stepped in after the two Turkish ministers to say the coup had completely changed the situation.
"The whole follow up of the attempted coup has caused some concerns among member states and that is why member states decided in December not to open any new chapters," said the Austrian, who has been sharply critical of Turkey's crackdown.