US Secretary of State Mike Pompeo met Greek Foreign Minister Nikos Dendias as tensions between Greece and Turkey increased.
"The United States and Greece shared views on the eastern Mediterranean and reaffirmed their belief that maritime delimitation issues should be resolved peacefully," the two countries said in a joint statement after Mr Pompeo met with Greek Foreign Minister Nikos Dendias.
Greece and the US, the statement said, "reiterated their dedication to enhancing their close cooperation as Nato allies, using all appropriate means at their disposal, in order to safeguard stability and security in the wider region." Relations between Greece and neighboring Turkey deteriorated sharply this year over disputed maritime boundaries and exploration rights in the eastern Mediterranean.
Arriving on Monday, Mr Pompeo stressed the importance of US relations with Greece and their shared views.
“Thrilled to be back in Greece, a vital US partner with whom we share a common strategic vision. The strength of our bilateral relationship is at an all-time high, and I’m looking forward to a productive visit,” he wrote on social media.
A dispute between Greece and Turkey over maritime borders and exploration rights in resource-rich waters in the eastern Mediterranean boiled over this year.
The two Nato allies have come close to direct confrontation after Turkey sent research vessel Oruc Reis into Greek waters with half a dozen warships. Greece responded by mobilising the bulk of its fleet.
While the Oruc Reis has now withdrawn, easing tensions, Turkey’s dispute with both Greece and Cyprus over the waters continued.
Nicosia has a separate dispute with Ankara over exploration rights in its waters.
The impositions of sanctions on Turkey by the EU, which has been drawn into the disagreement, have been wrangled over for weeks in Brussels.
Prior to his trip to the Greek city of Thessaloniki on Monday, Mr Pompeo spoke to Nato Secretary General Jens Stoltenberg about Greece and Turkey.
Nato has hosted discussions between the two nations at a technical level in recent weeks.
"Pleased to speak today with Nato Secretary General Jens Stoltenberg to discuss de-escalation of the situation in the Eastern Mediterranean and reiterate the importance of Nato alliance unity," Mr Pompeo tweeted on Sunday.
Mr Pompeo’s visit to Greece’s most populous city and then to Crete to visit the Souda Bay naval base has irritated Turkey.
The waters between Crete and Cyprus lie at the heart of the dispute.
Earlier this month, Turkey said the United States needed to return to a neutral stance on Cyprus, after Washington and Nicosia signed an agreement to open a training centre.
During a visit to Cyprus, which also provoked discontent, Mr Pompeo said that the United States would lift a 33-year arms embargo on Cyprus and improve its security co-operation with Nicosia.
The eastern Mediterranean island was split in a Turkish invasion in 1974 triggered by a brief Greek-inspired coup. Only Ankara recognises the self-declared government in the north of the country.
Mr Pompeo is the first US secretary of state to visit Thessaloniki. The stop is the first leg of a five-day trip to Europe, which includes visits to Italy, the Vatican and Croatia.
During his visit to Thessaloniki, the US diplomat also signed a bilateral science and technology agreement, as well as hosting energy sector business leaders for a discussion to highlight diversification and infrastructure projects in Greece. He will also join members of the city's Jewish community to commemorate Yom Kippur.