Ukrainians in the industrial cities and resort villages along the coast of the Sea of Azov knew a showdown with Russia was coming. The only question was when.

Even before the clash on Sunday in which Russia’s coastguard seized three Ukrainian ships, Moscow had spent months strangling the sea trade into the vulnerable Ukrainian port cities between mainland Russia and Crimea.

Now, Kiev has said that several key cities are under an effective sea blockade, with ships trapped at ports such as Mariupol and Berdyansk, resulting in millions of hryvnia in lost revenues, and loading cranes standing idle.

For six days now, ships unloading grain and metal have been stranded in the icy waters near Berdyansk, a port and resort town, waiting in vain for permission from Russia to pass through the Kerch strait. There is no other way in or out of the Sea of Azov.

“It began this summer, the Russian federation’s answer to us,” said Alexander Barchan, the head of the Berdyansk sea port authority, in an interview at his offices by the docks. Year on year, he said, shipping had already dropped 50%. “I think we can safely call it an economic blockade. We’re losing cargo flow, we’re losing profit. We’ve moved just half the cargo that we did in previous years.”

Russia has denied any disruption to Ukrainian shipping. Asked how long it could continue, Barchan paused, put up his hands and said: “We don’t even want to speculate.”

The emergence of a naval front has ignited concerns that the simmering conflict between Russia and Ukraine could lead to open war. Tensions rose this summer after Russia completed a 12-mile bridge spanning the Kerch strait to allow a direct driving route to annexed Crimea without entering Ukraine.

The Ukrainian president, Petro Poroshenko, on Thursday called for Nato to send ships to the Sea of Azov to support Ukraine and break the blockade.

The slowdown is similar in nearby Mariupol, where the port helps feed the hulking steel and iron factories that give the city its sour smell. “It’s gone from a trickle to just nothing,” is how one port official described the number of ships entering and leaving. The city of 500,000 has spent four years on the frontline of Ukraine’s conflict with Russian-backed separatists. Deadly trench fighting continues just 12 miles to the east.

Facebook Twitter Pinterest The seaport in Mariupol. Photograph: Sergey Vaganov/EPA

As an icy wind swept Mariupol’s streets this week, Father Sergei sang prayers for a crowd of activists in front of a banner that read: “Russia is an aggressor country.” The vigil of 200 activists and former soldiers gathered in support of the 23 sailors captured by Russia on Sunday. The men have been charged in court, despite Ukraine’s protests that they should be treated as prisoners of war.

For the first time since the beginning of the war, Mariupol has been put in a state of emergency, along with 10 border regions across Ukraine. People here have met the decision with a sense of bemusement, having seen the city nearly fall to pro-Russian separatists in 2014. The following year, a salvo of Grad rockets slammed into apartment blocks in the city, killing 20.

“The danger here has never really gone away, we’ve only learned to live with it,” said Galina Odnorog, an activist and military volunteer who launched a campaign this summer to bring attention to Ukrainian ships being detained in the Sea of Azov.

On Wednesday, the Ukrainian minister of infrastructure, Volodymyr Omelyan, wrote that 18 ships, four going to Berdyansk and 14 to Mariupol, were being blocked by Russia from passing through the Kerch strait. Another 17 ships were stuck in the Sea of Azov and could not leave, Omelyan wrote.

“Only vessels moving toward Russian ports on the Sea of Azov are permitted entry,” Omelyan wrote. “In essence, Russia has blocked Ukrainian ports on the Sea of Azov.”

Facebook Twitter Pinterest Ukrainian students hold placards saying ‘Keep Calm and Stay Strong’ in Kiev. Photograph: Sergei Supinsky/AFP/Getty Images

Russia holds de facto control over the waters of the Kerch strait. It is bound by a 2003 treaty to allow Ukrainian ships access to the Sea of Azov. But since completing construction of the Crimean bridge, which took three years and cost $3.9bn (£3.05bn), Russia has implemented draconian checks on ships bound for Ukrainian ports, sometimes holding them for days.

More than just a symbol of control, the bridge also played a physical role in last week’s clash. After Russia’s coastguard engaged three Ukrainian ships, Russia swarmed the strait with military jets and helicopters, and even parked a container ship in front of the bridge under which ships pass, effectively shutting down the strait in a show of force.

For some, the clash vindicated months of warnings about Russia’s growing ambitions in the Sea of Azov. Ukrainians said that while western countries spoke about being “deeply concerned” but refused to intervene, Russia had essentially cornered Mariupol from the separatist east and now from the sea as well.

Ukraine president calls for Nato warships in Sea of Azov Read more

“Now for Russia, the Kerch bridge is like a jewel-pearl,” Oksana Syroyid, deputy speaker of Ukraine’s parliament, said in an interview in Kiev. “And Russia will protect it severely. I assume that for Russia the protection of the Kerch bridge is even more important than blocking Ukraine from the ports on Azov. Blocking the ports is a consequence of protecting the Kerch bridge.”

Facebook Twitter Pinterest The Crimean bridge across the Kerch strait. Photograph: Sergei Malgavko/Tass

In Mariupol, the implementation of martial law has changed little in day-to-day life. Armed guards still stand at the train station and at checkpoints in and out of the city alongside tank traps stencilled with flower graffiti.

“Generally people don’t start acting differently until the shooting starts,” said Odnorog, the former military volunteer.

But there was a sense that the events of the last week marked an important new stage in the conflict.

“It wasn’t little green men, it wasn’t some hybrid warfare,” said Dmitry Chichera, a local environmental activist who runs an open workspace in downtown Mariupol. “It was Russia attacking Ukraine acting under their own flag.”



