US President Barack Obama said in a press conference that Washington stood "ready to impose further sanctions" depending on whether Russia escalated or de-escalated the situation in Ukraine.

The sanctions came after the referendum in Crimea on Sunday in which more than 95 percent of voters answered ‘yes’ to the autonomous republic joining Russia. 

Crimea's lawmakers on Monday formally asked to join Russia and vowed to disband Ukrainian military units stationed across the peninsula

According to a White House announcement, US imposes financial sanctions on seven top Russian government officials and lawmakers in reprisal for Crimea referendum.

The White House said Ukraine's ousted pro-Kremlin president Viktor Yanukovych and Crimea's self-declared premier Sergiy Aksyonov were both on the US list.

The Russians targeted include upper house of parliament speaker Valentina Matviyenko and Deputy Prime Minister Dmitry Rogozin -- responsible for overseeing Russia's military and industrial sector.

"These are clearly people who are very close to President (Vladimir) Putin," said one US official on condition of anonymity.

A second US official called the steps "by far the most comprehensive sanctions applied to Russia since the end of the Cold War."

Those listed will see any assets and interests in the United States or under US jurisdiction blocked.

They will also be banned from doing business with Americans and will find it difficult to make financial transactions using dollars.

Dimitry Rogozin -- a former Moscow envoy to NATO -- ridiculed the US maneuvers.

"I think some prankster prepared the draft of this Act of the US President," Rogozin tweeted in English.
   
Earlier European Union foreign ministers also agreed to impose travel bans and asset freezes against 21 Russian and Ukrainian officials claimed responsible for an independence referendum in Crimea.

RA/NJF