THESSALONIKI, Greece (AP) — U.S. Secretary of State Mike Pompeo met with Greek Foreign Minister Nikos Dendias in the northern Greek city of Thessaloniki Monday, the first leg of a five-day regional tour that will include Italy, the Vatican and Croatia.

Tension in the eastern Mediterranean is to feature prominently during Pompeo's two-day stay in Greece, which will include a visit to the Souda Bay naval base on the southern island of Crete Tuesday.

Frequently testy relations between Greece and neighboring Turkey have deteriorated sharply this year, particularly over maritime boundaries and exploration rights in the eastern Mediterranean. The dramatic escalation in tension led to fears of war between the two NATO members.

Turkey sent a research vessel, accompanied by warships, to prospect for energy resources in an area Greece claims is on its own continental shelf and where it claims exclusive economic rights. Athens sent warships of its own to the area.

European Union members are to discuss imposing sanctions on Turkey for its actions.

Pompeo and Dendias made no statements after their meeting, which lasted just under an hour.

The U.S. Secretary of State had discussed the situation in the eastern Mediterreanean late Sunday with NATO Secretary-General Jens Stoltenberg as he headed to Greece.

“Pleased to speak today with @NATO Secretary General @jensstoltenberg to discuss de-escalation of the situation in the Eastern Mediterranean and reiterate the importance of NATO Alliance unity,” Pompeo tweeted.

Amid the tension, Greece has announced major arms purchases, including fighter jets from France, as well as warships, helicopters and weapons systems.

Last October, Pompeo visited Athens and signed a revised defense cooperation agreement with Greece that provided for increasing joint U.S.-Greece and NATO activity at three locations in Greece as well as infrastructure and other improvements at Souda Bay.

Pompeo is the first U.S. Secretary of State to visit Greece’s second largest city of Thessaloniki. Security was tight in the port city, with the venue of Pompeo's meeting with Dendias changing from the originally planned location, a local ministry, to a hotel for security reasons, authorities said. A protest against his visit was planned for Monday evening.

During his visit to Thessaloniki, Pompeo is to sign a bilateral science and technology agreement, as well as host energy sector business leaders for a discussion to highlight energy diversification and infrastructure projects in Greece. He will also join members of the city’s Jewish community to commemorate Yom Kippur.

Pompeo will depart later Monday to Crete, where he is also scheduled to meet with Greek Prime Minister Kyriakos Mitsotakis.