ATHENS, Greece — Third countries may be invited to talks aimed at easing a dispute between Greece and Turkey over energy rights that has brought warships to the eastern Mediterranean, a top European Union official said Tuesday. Greece and Turkey have been involved in a standoff at sea for weeks over maritime boundaries between Turkey’s coast, the ethnically divided island nation of Cyprus and several Greek islands. A Turkish research ship that has been operating in the area over which Greece claims exclusive rights has returned to port for maintenance, giving EU diplomats a window to launch negotiations between Greece and Turkey. EU member countries are also mulling sanctions against Turkey over its exploration. European Council President Charles Michel said while visiting Athens that he was hopeful a commitment for talks would be made soon and that a negotiating process involving several countries could help facilitate an agreement. “We are discussing the idea of a multilateral conference because, beyond bilateral dialogue, there is probably the need to bring the different countries to the table in order to deal with the different issues,” Michel said. He did not elaborate. Germany, which currently holds the EU’s rotating presidency and launched an effort in July to broker direct Greek-Turkish negotiations, is a likely candidate to participate if the discussions are broadened, while Greek officials say they also want the Republic of Cyprus

NATO has also organized contacts between Greek and Turkish military officials in hope of preventing the use of force in the disputed area of the eastern Mediterranean. Turkish defense officials said that a new round of NATO-facilitated contacts took place Tuesday. In recent days, both sides have expressed willingness to attend negotiations. “We must leave gunboat diplomacy aside and join a genuine dialogue within the framework of international law and with respect for good neighborly relations,″ Greek Foreign Minister Nikos Dendias said. The two countries have sent warships as part of an armed forces buildup that has included multiple military exercises.

The European Union’s top foreign affairs official, Josep Borrell, said the bloc’s relations with Turkey were at a “watershed moment.”

“Tension has been continuing to rise over the summer. I have spent the last few months, including this summer, trying to facilitate the de-escalation efforts,” Borrell said in Brussels. “But the least I can say is that more efforts are needed — the softest way of saying that the situation has not been improving.”

However, he noted that the return of the research vessel to port was a step in the right direction.”

Domestically, Borrell said, Turkey “is seriously backsliding away from European Union values and reforms.” Specifically, he said, the country had not delivered on promises to strengthen the independence of the judiciary.

“We perceive a worrying backsliding in the area of rule of law and fundamental freedoms that continues to raise our concerns,” he said.

Raf Casert in Brussels and Zeynep Bilginsoy in Istanbul contributed.