A top Seante Republican on Thursday accused Russian President Vladimir Putin of trying to seize key Ukrainian cities that would grant him a “land bridge” to the annexed peninsula of Crimea.

“That strategy is very clear,” Wisconsin Sen. Ron Johnson, who chairs the Foreign Relations subcommittee for Europe, told the Washington Examiner. “It’s pretty obvious what Putin’s doing.”

Johnson offered that assessment after a trip to Ukraine last weekend, where he met with President Petro Poroshenko to discuss the Russian military’s recent attack on three Ukrainian ships that tried to pass through the Kerch Strait into the Sea of Azov. Russia justified the move by claiming sovereignty of the land on both sides of the waterway as a consequence of the annexation of Crimea. Poroshenko forecast that Putin is pursuing a step-by-step effort to take the rest of the Ukrainian land around the sea, to establish an overland route to Crimea.

“This is what Poroshenko laid out for me very clearly, Putin's strategy,” said Johnson, who co-sponsored a Senate resolution condemning Russia over the Kerch Strait incident last month.

That assessment echoes the view from Estonia, a nearby NATO ally that keeps a watchful eye on Russian maneuvering in the region. The sea of Azov, which provides access through the Black Sea to the Mediterranean and the open ocean, is home to a pair of significant Ukrainian port cities — Berdyansk and Mariupol. “Now the next step for Putin is, let's start choking off maritime activity to those Ukrainian ports to dramatically harm and effect the economy in those two port cities, which could potentially set up the next step of the land bridge from Russia into Crimea,” Johnson said.

Russia launched a stealthy invasion of territory adjacent to those cities, under cover of ethnic Russians living in Crimea and other parts of eastern Ukraine. Mariupol likewise has a major Russian-speaking population, contributing to NATO suspicions that Putin still has an appetite for territorial expansion.

“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 kind of social upheaval there,” Permanent Secretary Kristjan Prikk, the top civilian in the NATO member’s Ministry of Defense, told the Washington Examiner in a recent interview.

“There are many important military equipment factories there, for in particular [the] navy, but some others as well,” Prikk added. “Mariupol has strategic significance both for Ukraine and as a target potentially for Russia.”

Johnson is urging White House national security adviser John Bolton and senior State Department officials to orchestrate a show of Western military force in the region. He wants a “multinational” flotilla of western warships — perhaps hailing from the United States, France, and the United Kingdom — to sail into the Black Sea.

“If not, I think Russia will view that as a real sign of weakness,” the senator said. “I don't want to see a hot war. I don’t want to see a gun fired ... [but] we need to put him on notice, we're not going to allow that to happen.”