BRUSSELS - Josep Borrell, the European Union (EU) high representative for foreign affairs and security policy, warned on Tuesday that EU's relations with Turkey were at a watershed moment in history.

At a European Parliament plenary, Borrell called for urgent and collective engagement to deal with the situation in the Eastern Mediterranean.

The dispute over Turkish natural gas explorations off Greek islands in the Eastern Mediterranean has escalated in recent weeks.

Greece considers the explorations illegal. The Turkish government, on the other hand, believes the waters, in which natural gas is being drilled on a trial basis, belong to the Turkish continental shelf.

"I have spent the last few months trying to facilitate de-escalation efforts. But the least I can say is that more efforts are needed -- the softest way of saying that the situation has not been improving," Borrell said to MEPs.

He said Turkey is an important neighbor of the EU, but with its actions in the Eastern Mediterranean its future relations with the bloc are called into question.

"Our relations with Turkey, which are -- I can say that firmly -- at a watershed moment in history," Borrell said.

According to the EU foreign policy chief, immediate de-escalation is essential to allow the resumption of dialogue and the negotiations, which is the only path towards stability and lasting solutions.

"This is one of the moments in history when decision makers have to go and face difficult decisions, trying to look for the best for all of us. I am sure that this is what the European Council will try to do at the next meeting," he said, referring to the Special European Council on Sept 24-25.

According to Borrell, the latest move by Turkey to discontinue seismic exploration in the waters is a step in the right direction and gives some hope that it will lead to further steps towards dialogue. "We are not going to solve it by military means, but through dialogue and negotiations," said the EU foreign policy chief.