U.S. Secretary of State Antony Blinken was meeting the leaders of Turkey and Greece on Saturday at the start of a week-long trip aimed at calming tensions that have spiked across the Middle East since Israel’s war with Hamas began in October.

The Biden administration’s most senior diplomat held talks with Turkey’s Foreign Minister Hakan Fidan in Istanbul and is scheduled later to meet President Tayyip Erdogan, a strong critic of Israel’s military actions in Gaza.

The talks are also expected to cover Turkey’s process to ratify Sweden’s membership of NATO, according to a senior State Department official traveling with Blinken.

U.S. officials have been frustrated by the lengthy process but are now confident that Ankara will soon approve Sweden’s accession to the alliance after the Turkish parliament’s foreign affairs commission backed the bid last month, said the official, speaking on condition of anonymity.

U.S. lawmakers have held up the sale of F-16 fighter jets to Turkey until it signs off on the addition of Sweden to the North Atlantic Treaty Organization. Sweden, which, along with Finland, applied to join NATO following Russia’s invasion of Ukraine in early 2022, would become the alliance’s 32nd member. Finland joined last year.

Blinken will later travel to the island of Crete to meet Greek Prime Minister Kyriakos Mitsotakis. Fellow NATO member Greece is awaiting the approval by the U.S. Congress of a sale of F-35 fighter jets.

“We’ll be discussing this issue. I think there will be positive developments,” Greek Foreign Minister George Gerapetritis told Greek Skai television.

Blinken’s tour in the coming days will include Arab states, Israel and the occupied West Bank, where he will deliver a message that Washington does not want a regional escalation of the Gaza conflict.

The war began when Palestinian Hamas militants attacked Israel on Oct. 7, killing 1,200 people and taking 240 hostages.

Israel’s retaliatory offensive has killed 22,600 Palestinians, according to Palestinian officials, and the conflict has spilled into the West Bank, Lebanon and Red Sea shipping lanes.

Blinken also hopes to make progress in talks on how Gaza could be governed if and when Israel achieves its aim of eradicating Hamas.

Washington wants regional countries, including Turkey, to play a role in reconstruction, governance and potentially security in the Gaza Strip, which has been run by Hamas since 2007, the official said.