U.S. President Barack Obama ordered a one-year extension of visa bans and asset freezes imposed on Russian government officials and others involved in the crisis in Ukraine.

The sanctions imposed in an executive order last March remain necessary because the Russian government’s actions “including its purported annexation of Crimea and its use of force in Ukraine, continue to pose an unusual and extraordinary threat to the national security and foreign policy of the United States,” Obama said in a notice to Congress published by the White House on Wednesday.

Individuals affected by the measures include Russian presidential adviser Sergey Glazyev, presidential aide Vladislav Surkov, Deputy Prime Minister Dmitry Rogozin, Federation Council Speaker Valentina Matviyenko, former Ukrainian President Viktor Yanukovych and Prime Minister of Crimea Sergey Aksyonov. 

The sanctions, announced after Crimea's unification with Russia in March 2014, would have expired automatically without the decision to renew them. The U.S. introduced further penalties in July after the conflict erupted between pro-Russian separatists and government troops in eastern Ukraine.