ISTANBUL — Greek coast guard ships opened fire on a cargo vessel sailing in international waters in the Aegean Sea, the Turkish coast guard said, escalating tensions between the regional rivals that have mounted in recent weeks.

There were no casualties in the shooting 11 nautical miles (13 miles) southwest of the Turkish island of Bozcaada on Saturday, the Turkish statement said. It added that after “harassment fire” from two Greek coast guard vessels, two Turkish coast guard ships went to the area and the Greek boats left.

Calls to the Greek Embassy in Ankara went unanswered Sunday, and it wasn’t clear why the gunfire occurred.

The neighboring countries have been embroiled in disputes for decades and frictions have ratcheted up in recent weeks, with both sides alleging airspace violations. Greek officials have raised concerns about another outbreak of conflict in Europe, following Russia’s war in Ukraine.

Turkey says Greece is breaking international agreements by keeping a military presence on islands close to Turkey’s Aegean coastline. It also has accused Greek air defenses of locking on to Turkish fighter jets during NATO exercises over the eastern Mediterranean.

Greece says it needs to defend its eastern islands — including tourist hotspots Rhodes and Kos, which are much closer to Turkey than to the Greek mainland — against its larger and militarily stronger neighbor.

Video footage from Saturday purportedly shows a Greek coast guard ship alongside the Comoros-flagged ship Anatolian as the sound of about a dozen gunshots are heard. A crew member speaks in Turkish, saying they are being attacked by the Greek coast guard.

The video, which was released by the Turkish coast guard and seems to have been filmed on a cellphone, shows what appears to be a bullet hole in a window and in the ceiling of the cargo ship’s bridge.

The Turkish statement said the gunfire was “in disregard of the rules of international law.” The 18 crew of the Anatolian consisted of six Egyptians, four Somalis, five Azerbaijanis and three Turks.

A Turkish prosecutor ordered an investigation. The country also has protested to Greek authorities, with Ankara demanding a swift investigation and explanation.

The Anatolian was anchored Sunday in the Dardanelles Strait off the Turkish coast, the state-run Anadolu news agency reported.

This week, the Greek government wrote letters to NATO, the European Union and the United Nations, asking them to formally condemn increasingly aggressive talk by Turkish officials and suggesting that tensions could escalate into open conflict.

Greek Foreign Minister Nikos Dendias said the behavior of Turkey — also a NATO member — risked “a situation similar to that currently unfolding in some other part of our continent,” referring to the war in Ukraine.

The Marine Traffic website, which monitors global shipping, says the Anatolian was previously named the Mavi Marmara. Israeli commandos stormed the vessel — then a passenger ship — in 2010 as it attempted to break a blockade on the Palestinian enclave of Gaza, killing nine Turkish activists, including a dual American citizen.

The Mavi Marmara incident led to a serious diplomatic rift between Israel and Turkey, which withdrew its ambassador to Israel and scaled back military and economic ties. Israel later apologized for the deaths and agreed to compensate the victims’ families.

In its entry for the Anatolian, Marine Traffic carried photographs of the Mavi Marmara with Turkish and Palestinian flags hanging from its sides. The website’s last recorded location for the Anatolian was in the Somali capital Mogadishu in late June.