WASHINGTON — President Barack Obama declared today that a referendum in 10 days on the future of a Ukraine’s Crimea peninsula would violate international law.

The United States also moved to impose visa restrictions and financial sanctions on Russians and Ukrainians for the moves Moscow already has made into Crimea.

Speaking from the White House, Obama said any decisions on the future of Crimea, a pro-Russian area of Ukraine, must include the country’s new government.

“The proposed referendum on the future of Crimea would violate the constitution and violate international law,” Obama said. “We are well beyond the days when borders can be redrawn over the heads of democratic leaders.”

Obama spoke hours after a March 16 date was set for a referendum on whether the region should become part of Russia.

Russian forces began moving into Crimea about a week ago, despite Obama’s warnings that there would be costs for such actions. Seeking to follow through on that threat, Obama moved today to enact new visa restrictions on an unspecified and unidentified number of people and entities that the U.S. accused of threatening Ukraine’s sovereignty and territorial borders.

The restrictions were unlikely to directly target Russian President Vladimir Putin.