The European Union and the United States have threatened to impose visa bans on at least 13 prominent Russian politicians and businessmen in the event that Crimea, the autonomous region in southern Ukraine, passes a referendum on Sunday to join the Russian Federation. 

Reuters reported that the Bild newspaper of Germany, citing diplomatic sources in Brussels and Washington, said the targeted list includes Defense Minister Sergei Shoigu, Deputy Prime Minister Dmitry Rogozin, chief of the presidential administration Sergei Ivanov, secretary of the National Security Council Nikolai Patrushev, and various other close associates of President Vladimir Putin, including Federal Security Service chief Alexander Bortnikov. In addition, Alexei Miller, the chief executive of Russian energy giant Gazprom (OTCMKTS:OGZPY), and Igor Sechin, boss of Rosneft (LON:ROSN), Russia's biggest crude oil producer, may also be hit with the ban. The Bild article is to hit newsstands Saturday.

Western European governments and the White House are gravely concerned about the referendum under which Crimea would secede from Ukraine, making it the worst crisis on the continent in decades. German Chancellor Angela Merkel has called the referendum “illegal and incompatible with Ukraine’s constitution.” Last week, European Council President Herman Van Rompuy warned that if Moscow does not pull its troops out of Crimea, it will “seriously affect the relations between the EU and Russia.” “If there is no de-escalation, the EU will decide on additional measures, such as visa restrictions, asset freezes and cancellation of the Russia-EU summit,” Rompuy said at a press conference. David Cameron, Britain’s Prime Minister, also threatened to impose asset freezes and travel bans on top Russians “relatively quickly,” while French President Francois Hollande called for economic sanctions against Russia.

In preparation for such possible sanctions, Russian Foreign Ministry spokesman Aleksandr Lukashevich said last week that his government would “react” to any moves by EU nations to prohibit or limit the movements of Russian travelers. “Should consular posts of any of the EU member countries move toward a certain tightening of visa application proceedings, we will immediately react to that,” he said, according to Russia Today. “It is obviously a politicized, unconstructive and baseless approach, which goes contrary to the existing agreements between Russia and the EU on further simplification of rules for mutual citizens’ travels.”

Putin himself warned that sanctions on any Russians would be equally harmful to Western Europe. “I believe that in the modern world, where everything is interconnected and interdependent, it is possible to cause damage to another country, but this will be mutual damage and one should bear this in mind,” he said.