Greece says it is ready for talks with Turkey over contested Mediterranean waters if Ankara continues “disengaging itself” from the crisis, following the withdrawal of a Turkish exploration vessel from a disputed region.

“Turkey still has time – ahead of and after the (EU) summit – to continue the first encouraging step of disengaging itself from this crisis,” Greek Prime Minister Kyriakos Mitsotakis said after talks with EU Council President Charles Michel in Athens, referring to the upcoming September 24-25 EU summit.

“If we have tangible proof and this (proof) is continued, we are ready to start immediately – I stress that, immediately – exploratory talks with Turkey regarding our only major dispute: the demarcation of maritime zones” in the Aegean and the eastern Mediterranean, he said.

The long-running dispute between the two NATO members flared up again last month when Turkey sent a ship, the Oruc Reis, to survey waters claimed by Greece. Greek and Turkish warships shadowing the boat collided, highlighting the potential for military escalation.

The European Union said Ankara could face sanctions, a move Turkey has decried as lacking legal basis.

On Sunday, less than two weeks before EU leaders discuss the crisis, the Oruc Reis returned to port.

Turkey said it would resume work after regular maintenance, but a senior Turkish official said it could stay longer to give diplomacy a chance.

The two countries had been on the verge of resuming talks last month, following mediation by Germany, but Turkey broke off contact after Greece and Egypt signed a deal which Ankara said violated its own claims.

Germany, which currently holds the EU presidency, has continued its diplomatic efforts, according to the Turkish official who spoke on condition of anonymity, and Turkey wanted to give those efforts a chance of success.

Maintenance work on the Oruc Reis could be finished in a week, allowing it to return to the disputed area, “but it can remain docked longer to reduce tensions in the region and allow for diplomacy”, the official said.

He said Turkey wanted to give an opportunity for EU foreign ministers, who meet on Monday, ahead of the summit, to take steps towards easing the crisis.

“Greek officials have also made statements softening the atmosphere. These are positive. We need to take steps forward for the solution of the problem now, without … pre-conditions.”

Greek and Turkish military officials were holding separate “de-confliction” talks at NATO headquarters on Tuesday. The meeting was one of a series of contacts aimed at preventing any incident at sea spilling over into open conflict, but was not expected to address the actual disputes.

Despite calling Oruc Reis back to port, Turkey still has a drilling ship and a seismic survey vessel operating in waters claimed by Cyprus, which is demanding EU sanctions on Ankara.

Meanwhile, Michel said third countries might be invited to talks aimed at easing the dispute.

Michel said he was hopeful a commitment for talks would be made soon and 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.

Prime Minister Mitsotakis called for European “solidarity” on the issue and a renewed migrant crisis.

Turkey’s foreign minister Mevlut Cavusoglu said his country has been proposing to restart exploratory talks with Greece.

“Exploratory talks actually cover all disputed issues between Turkey and Greece … The previous government [in Greece] … didn’t want to actually restart. And this government also has not been willing to restart the exploratory talks, so we have to make an agreement,” he said.

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.