WASHINGTON — In the most comprehensive sanctions against Russia since the end of the Cold War, President Barack Obama on Monday froze the U.S. assets of seven Russian officials, including top advisers to President Vladimir Putin, for their support of Crimea’s vote to secede from Ukraine.

The Treasury Department also is imposing sanctions on four Ukrainians — including former President Viktor Yanukovych and others who have supported Crimea’s separation — under existing authority under a previous Obama order. Senior administration officials also said they are developing evidence against individuals in the arms industry and those they described as “Russian government cronies” to target their assets.

Obama was to make a statement Monday from the White House.

The administration officials said Putin wasn’t sanctioned despite his support of the Crimean referendum because the U.S. doesn’t usually begin with heads of state. But the officials say those sanctioned are very close to Putin and that the sanctions are “designed to hit close to home.”