The United States has “more advanced” technology than Russia’s nuclear-powered cruise missile that was presumed to have been involved in a mysterious accident last week, President Donald Trump has said.

At least five nuclear experts were killed in the secretive rocket engine test at sea in northern Russia five days ago. U.S.-based experts and intelligence officials have since said they suspect the mishap occurred during testing of the Burevestnik nuclear-powered cruise missile, which has been touted by Russian President Vladimir Putin and designated as SSC-X-9 Skyfall by NATO.