WASHINGTON, March 16 -- The United States on Monday vowed to keep in place sanctions imposed over what it called Russia's "occupation" of the Crimean Peninsula.

State Department spokeswoman Jennifer Psaki dismissed as "sham" the referendum held a year ago on the peninsula, in which 95.5 percent of voters voted to rejoin Russia.

"The United States reiterates its condemnation of a vote that was not voluntary, transparent, or democratic," she said in a statement. "We do not, nor will we, recognize Russia's attempted annexation and call on President (Vladimir) Putin to end his country's occupation of Crimea."

Washington responded then to Moscow's annexation by slapping sanctions first on seven Russian and four Ukrainian officials, and then expanding the measures three days later to cover some of Putin's allies and a Russian bank.

"This week, as Russia attempts to validate its cynical and calculated 'liberation' of Crimea, we reaffirm that sanctions related to Crimea will remain in place as long as the occupation continues," Psaki said in her statement.

"Russia used its military to forcibly seize and occupy Crimea, sovereign Ukrainian territory, and then staged an illegal so- called referendum in a feeble attempt to justify its actions," she told reporters at a daily news briefing.

She once again accused Russia of engaging in "destabilizing activities" in eastern Ukraine, where continuing fighting between the government troops and independence-seeking rebels have killed some 6,000 people.

The spokeswoman referred to a newly released documentary named "Crimea: The Way Home," in which Putin acknowledged Russian forces ' intervention in Crimea a year before.

"So it certainly brings into question the credibility of claims being made today that the Russian military is not intervening in eastern Ukraine," she said.

Washington and its European allies have slapped tough sanctions on Moscow over its alleged involvement in the conflict in Ukraine' s east, and have threatened more in case of its failure to implement a new peace deal.

The accord signed in February in the Belarusian capital of Minsk has not been fully implemented, with eastern Ukraine still besieged by sporadic fighting.