President Obama issued an executive order Monday imposing sanctions against seven senior Russian government officials after a Crimean referendum to secede from Ukraine and join Russia a day earlier.

Among the Russians being hit with economic punishments are Vladislav Surkov, an aide to Russian President Vladimir Putin, Sergey Glazyev, a Putin adviser, Leonid Slutsky, a State Duma deputy, Andrei Klishas, a member of the Council of Federation of the Federal Assembly of the Russian Federation, Valentina Matviyenko, head of the Federation Council, Dmitry Rogozin, deputy prime minister of the Russian Federation and Yelena Mizulina, a State Duma deputy.

Under the sanctions, any U.S. assets belonging to those individuals have been frozen and U.S. citizens are barred from conducting business with those people.

The U.S. government also issued sanctions Monday against separatist leaders Sergey Aksyonov, the Crimean prime minister, Vladimir Konstantinov, speaker of the Crimean parliament, former Ukrainian presidential chief of staff Viktor Medvedchuk and former Ukrainian President Viktor Yanukovych.

“Today’s actions send a strong message to the Russian government that there are consequences for their actions that violate the sovereignty and territorial integrity of Ukraine, including their actions supporting the illegal referendum for Crimean separation,” the White House said, announcing the sanctions.

“Our focus is to identify these cronies of the Russian government and target their personal wealth, but not companies that they may manage on behalf of the Russian state,” a senior administration official explained in a conference call with reporters Monday.

The European Union also issued sanctions against 21 people involved in the Crimean referendum.

Putin is scheduled to address the Crimean vote on Tuesday, when U.S. officials expect him to endorse the annexation of the region into Russia.

“There will be further costs if there are further steps,” a senior administration official warned if Putin takes such an action.

Putin was not among those sanctioned but senior administration officials said the new restrictions would "hit close to home" for the Russian president.

"We do not begin these types of sanction efforts with a head of state," a senior official explained.

The Obama administration downplayed questions over whether the sanctions would lead to retaliation from Russia and potentially harm the U.S. economy.

"Frankly, Russia stands a lot more to lose from political and economic isolation than the United States," a senior administration official said, pointing to the battering the Russian stock market has taken since the crisis began.

"The world is with us," the official added.

Russia’s military takeover of Crimea sparked an international crisis, but the U.S. and allies have been unable to dissuade Putin to work toward a negotiated diplomatic solution.

Moscow says it is trying to protect the safety of the region’s Russian-ethnic majority, but the Obama administration sees Putin’s moves as a power grab.

In a phone call Sunday, Obama told Putin that the international community would not accept the legitimacy of the Crimean vote to secede and was “prepared to impose additional costs on Russia.”

The president has urged Moscow to reject the referendum, pull back military troops, allow international monitors into Crimea and sit down for talks with the interim government in Kiev.

This story was published at 9:57 a.m. and has been updated.