Russia might be angling to take control of the key Ukrainian port city of Mariupol, a top Estonian defense official told the Washington Examiner, forecasting a move that would mark a serious escalation of the simmering conflict between the two neighbors.

“This is part of Ukraine that has economic problems and social problems because of the conflict anyway, and so by squeezing the access to this area of Ukraine, they are making the social or economic conditions even worse and possibly, possibly trying to create some kid of social upheaval there,” Permanent Secretary Kristjan Prikk, the top civilian in the NATO member’s Ministry of Defense, told the Washington Examiner.

Prikk visited Washington just days after Russia seized three Ukrainian vessels in the Kerch Strait between the Black Sea and Azov.

He said that incident entails a “very direct escalation” of the Ukraine crisis because it marks the first open clash between Russian and Ukrainian forces since the 2014 annexation of Crimea. More than 10,000 people on all sides have been killed in the related fighting in eastern Ukraine, but Moscow portrays the conflict has an intra-Ukrainian fight between Kiev loyalists and ethnic Russian separatists while reiterating its sovereignty over Crimea.

Though Ukraine is not a member of NATO, Prikk and other officials from the Baltic region see real national security significance to the outcome of that conflict.

“In a way, I would say Ukraine is doing the fighting for us there. They are in direct contact with Russian Federation forces there,” the permanent secretary told the Washington Examiner. “They are the ones that from time to time also cause losses to them. So, we shouldn't neglect this conflict.”

The Kremlin isn’t neglecting it. Russian officials deployed a fourth battalion of S-400 anti-aircraft missile systems to Crimea on Thursday, according to a report from state-run media. One diplomat, speaking days prior to the Kerch Strait incident, warned of “an economic blockade, de facto” being imposed by Russia.

“It's part of the economic section of the hybrid warfare,” Prikk said.

That’s a reference to the Russian tactics, executed most dramatically in the invasion and annexation of Crimea by “elite troops, in conjunction with an information warfare campaign and the deployment of loyal Russian proxies,” as RAND Corporation’s Christopher Chivvis told the House Armed Services Committee last year.

The annexation of the peninsula gave Russia control of both sides of the Kerch Strait, which forms the basis now of a claim of total sovereignty over the waters. The extension of the fighting into regions of eastern Ukraine that neighbor the district around Mariupol has heightened the likelihood that Russia would seek total control of the lands surrounding the Sea of Azov, Prikk said.

"The overwhelming majority in the city of Mariupol, for example, the most important port city for the sea of Azov, is overwhelmingly Russian speaking,” Prikk observed. “There are many important military equipment factories there, for in particular [the] navy, but some others as well. Mariupol has strategic significance both for Ukraine and as a target potentially for Russia.”

Prikk stressed that Ukraine does not qualify for the right of collective defense that a member of NATO would enjoy, but he said that friendly ties between Western powers and Kiev need to be highlighted in order to deter Russia.

“I’m sure that inside the Russian calculus, there is definitely somewhere the good relationship between Ukraine and NATO and the [European Union],” Prikk said. “[They’re aware of the] risk that if they do something really ugly and really stupid, there will be even more sanctions put on them, there will be even more focus and willingness in assisting Ukraine in dealing with this crisis.”

Prikk declined to predict outright that Russia will try to seize Mariupol, either by conventional or hybrid means, in part because President Trump authorized the sale of anti-tank missiles and other lethal weapons to Ukraine, in addition to other Western support for Kiev. The Ukrainians are not an “easy target” anymore.

“The Ukrainian military today is very different from the military that they had in 2014,” Prikk said. “The Ukrainians have built, bought, [had] donated quite a lot of equipment. They've been putting heavy emphasis on mobility — anti-armor capabilities, communications ... It's definitely a credible fighting force.”

Prikk, speaking just a few days before Secretary of State Mike Pompeo meets with his NATO counterparts in Brussels, said Western powers need help to equip and train the Ukrainian military to repel the Russians while providing diplomatic support.

“Our utmost concern ... is to avoid a situation whereby that kind of land grabs or sea grabs or however it works would becomes sort of a normal part of this conflict cycle, where every couple of months or years there's a new spike whereby the aggressor is able to seize new areas, create new political reality, and get away without any punishment,” he said.