KASTELLORIZO, Greece — In the narrow Mediterranean strait between the easternmost islands of Greece and the shoreline of western Turkey, Kostas Raftis steered his fishing dinghy along the invisible maritime border dividing the two countries. Usually, this is a placid spot where Mr. Raftis fishes for red mullet and snapper. Now it is unexpectedly becoming a geopolitical flash point.
Last week, a low-flying Turkish helicopter had passed provocatively close to a military base on the nearby Greek island of Ro, drawing warning shots from soldiers. That incident was followed three days later by the death of a Greek fighter pilot who crashed, his government said, after attempting to intercept a Turkish aircraft that had entered the country’s airspace.
In all, the number of incursions by Turkish military ships and jets into Greek territory has spiked in recent months, according to Greek officials, stoking concerns of a new military conflict in a region where Turkey is already embroiled in the war raging in Syria.
The biggest uncertainty involves Turkey’s strongman president, Recep Tayyip Erdogan, and whether his ambitions are fueling renewed claims to these Greek isles — particularly after he embarked on Wednesday on an election campaign in which he is expected to play heavily on nationalistic sentiment.
“With the people of Turkey, we don’t have problems,” said Mr. Raftis, 58. “The problem is with Erdogan, with the Turkish government. They want to make Turkey bigger.”
Indeed, though the border issue has simmered for nearly a century, analysts worry that the unpredictable nature of Mr. Erdogan makes the situation more volatile than ever between the countries, nominal NATO allies, who almost fought a war over an uninhabited island in nearby waters two decades ago.
In December, to the surprise of his hosts, Mr. Erdogan used the occasion of the first visit to Greece by a Turkish president in 65 years to call for a redrawing of the border. That did not go down well.
In recent years, Mr. Erdogan has often stoked tensions overseas in order to bolster his domestic standing, insulting several European governments, deploying troops in Syria, and lashing out at the United States.
“Erdogan is a little bit out of control — he’s picking a lot of fights and there is a lot of uncertainty about how far he’s prepared to go,” said Nikos Tsafos, who researches the politics of the Eastern Mediterranean at the Center for Strategic and International Studies, a Washington-based think tank.
“The odds of something going wrong are increasing on a weekly basis,” he said.
The border issue has its roots in the collapse of the Ottoman Empire in the aftermath of World War I, and in subsequent international treaties that gave many islands that had once belonged to the Ottoman Empire — including Kastellorizo, the nearest permanently inhabited island to Ro — to other European powers.
Today, Turkey — which was formed from the rump of the Ottoman Empire — does not contest Kastellorizo’s sovereignty. But the government feels it is unfair that Greece should have the right to potentially exploit energy resources in parts of the Mediterranean seabed that lie within sight of Turkey but many hundreds of miles from the Greek mainland.
“At the fundamental level, there is a different perception of how the Aegean Sea should be treated,” Mr. Tsafos said.
Other recent developments have compounded the decades-old disagreement. Talks have broken down over the status of the island of Cyprus, which is divided between a Greek-backed and internationally recognized state in the south, and a Turkish-backed breakaway state in the north.
Greece declined to extradite eight Turkish servicemen who had fled following a failed coup in 2016; and the Turkish government has arrested two Greek border guards, seemingly in response.
“The potential for a military conflict between Greece and Turkey has never seemed as close since the 1990s,” said Soner Cagaptay, director of the Turkish Research Program at the Washington Institute for Near East Policy.
The Turkish government says Greece is to blame for the spike in tensions.
“The Greeks always want attention,” said a senior Turkish official who asked not to be named in accordance with Turkish protocol. “They’re like babies, and it’s always been like that.”
But statistics released by Greece suggest a different narrative. According to the Greek military, Turkish incursions into Greek airspace rose to 3,317 in 2017 from 1,269 in 2014, while maritime incursions rose to 1,998 from 371 in the same period.
The Greek and Turkish prime ministers, Alexis Tsipras and Binali Yildirim, appeared to calm tensions with a phone call after the two incidents over Ro last week.
But on Monday, the situation worsened again when Turkey said it had sent coast guards to remove several Greek flags that had been planted on an islet in a Greek island group within sight of the Turkish coast.
Less than 24 hours later, Mr. Tsipras had flown to Kastellorizo — nominally to open a desalination plant, but in reality to send a strong signal on Greek sovereignty.
“Greece can defend its sovereign rights from one end of this country to the other,” said Mr. Tsipras, as the cliffs of Turkey loomed in the distance over his right shoulder. “We won’t negotiate, we won’t bargain, we won’t cede an inch of Kastellorizo land.”
But Turkey did not seem to get the message. After Mr. Tsipras started his journey home, his helicopter pilot was radioed by Turkish air traffic controllers, who accused the pilot of flying into Turkish airspace, a Greek military official said.
After Mr. Erdogan raised the issue of redrawing the border during his December visit, the Greek defense minister, Panos Kammenos, accused the Turkish leadership of stupidity, described its military as enfeebled, and reminded Turkey of a humiliating Ottoman defeat in the 19th century.
In response, Mr. Yildirim taunted Greece over its retreat from Asia Minor in 1922, while the leader of the Turkish opposition, Kemal Kilicdaroglu, attempted to go one better by suggesting that Turkey invade no less than 18 Greek islands.
Were such an unlikely scenario to occur, Kastellorizo and Ro would most likely be on Mr. Kilicdaroglu’s list.
Ro is a hallowed place for many Greek patriots: In 1927, a woman from an old Kastellorizo family, Despina Achladioti, moved there and kept a Greek flag flying until her death in 1982 — enshrining her in national folklore as “the Lady of Ro.” Local girls wearing traditional clothes at the opening of a desalination plant attended by Mr. Tsipras.Credit…Eirini Vourloumis for The New York Times “Until we see a Turkish military boat in the port of Kastellorizo, we will not be scared,” said Dimitris Achladiotis, the island’s deputy mayor.Credit…Eirini Vourloumis for The New York Times
But some Turkish nationalists believe these islands are “so close to the Anatolian land mass that they should belong to Turkey not Greece,” said Sinan Ulgen, a Turkey analyst at Carnegie Europe, a Brussels-based research group, and a former Turkish diplomat.
For all the rhetoric, many of Kastellorizo’s 300 permanent residents, as well their Turkish neighbors across the water, feel the tensions have been exaggerated by the news media — and by attention-seeking politicians. For example, none of them saw or heard the helicopter incident.
“We’ve had news like this for years, but we’ve never had an actual problem,” said Dimitris Achladiotis, the island’s deputy mayor, who is a great-nephew of the Lady of Ro. “Until we see a Turkish military boat in the port of Kastellorizo, we will not be scared.”
Further round the island’s horseshoe harbor, a bar owner told the story of how he met his Turkish wife in Kas, the Turkish town that lies a short ride across the sea. Many Kastellorizo residents buy their weekly shopping from Kas’s market on Fridays, while a ferry service brings more than 20,000 people in the other direction every year. And the two communities cement their friendship with an annual swimming race.
“We all coexist and are similar in lots of respects,” said Kikkos Magiafis, the bar owner with a Turkish wife. “We have a very similar culture.”
This was a sentiment echoed in Kas, even among Turkish nationalists. The islanders on Kastellorizo “are normal people like us, civilians living their lives like us,” said Ismail Sah Yilmaz, the head of the local branch of the Iyi Party, a Turkish nationalist group.
But strolling along the quay at Kastellorizo on Tuesday, patting a few toddlers and listening to their parents’ gripes about island life, Mr. Tsipras appeared to have other ideas.
“You are the guardians of Thermopylae,” he told several islanders — though presumably he did not mean it literally.
At the Battle of Thermopylae in 480 B.C., a few hundred Greeks held off tens of thousands of soldiers from the East before, according to myth, being betrayed and slaughtered.
Iliana Magra contributed reporting from Kastellorizo, and Niki Kitsantonis from Athens.A version of this article appears in print on April 22, 2018, Section A, Page 6 of the New York edition with the headline: Incursions By Turkey Put Greece On Alert.