(Corrects to 20 more Russians hit from 19 in second paragraph)
MOSCOW, March 20 (Reuters) - President Vladimir Putin's spokesman said on Thursday it was "unacceptable" for the United States to impose sanctions on Russians and warned Moscow would respond in kind to U.S. measures meant to punish allies of Putin.
Spokesman Dmitry Peskov said the Kremlin was studying a list of 20 more Russians hit with U.S. visa bans and asset freezes over Russia's annexation of Ukraine's Crimea region. The United States had designated 11 Russians and Ukrainians on Monday.
"The appearance of some of the names on the list causes nothing but extreme perplexity," Peskov said. "But no matter what the names are, the practice of (issuing sanctions) lists is unacceptable for us.
"In any case, Russia's reaction to these lists will be based on the principle of reciprocity and will not be long in coming."
Peskov spoke shortly after the Foreign Ministry listed nine U.S. officials and lawmakers barred from Russia in retaliation to the initial U.S. list.
Putin signed a treaty to make Crimea part of Russia on Tuesday. Russia's seizure of military control of Crimea and moves to annex it have caused the most serious East-West crisis since the Cold War. (Reporting by Maria Kiselyova; Writing by Alexei Anishchuk; Editing by Steve Gutterman and Mark Trevelyan)