Thirteen U.S. senators have written to FIFA, soccer's world governing body, urging the organization to replace Russia as host of the 2018 World Cup.

Senators Robert Menendez (Democrat-New Jersey) and Ron Johnson (Republican-Wisconsin) organized the letter, released on April 1, calling on FIFA to move the soccer championship because of Russia's "ongoing violations of the territorial integrity of Ukraine."

Nine Republicans -- including former presidential candidate John McCain -- and four Democrats signed the letter.

"Allowing Russia to host the FIFA World Cup inappropriately bolsters the prestige of...[Russian President Vladimir Putin's]...regime at a time when it should be condemned," the senators said.

FIFA has thus far rejected calls for the event -- one of the world's top sporting events -- to be moved away from Russia.

Russia illegally annexed Ukraine's Crimean Peninsula in March 2014 and is accused by Ukraine, Western countries, and NATO of backing pro-Russian separatists in eastern Ukraine, a charge Moscow denies.