European Union foreign ministers slapped travel bans and asset freezes Monday on 21 people from Russia and Crimea who they linked to the push for the secession of Ukraine's strategic Black Sea peninsula.

The sanctions came hours after Crimea's parliament declared the region an independent state, following its residents' overwhelming vote Sunday to break away from Ukraine and seek to join Russia.

The ministers meeting in Brussels did not immediately release the names of those targeted by the sanctions.

Two diplomats said the sanctions targeted 13 Russians and eight people from Crimea. The diplomats spoke on condition of anonymity because the breakdown of the nationalities had not been officially announced.

The 28-nation EU and the United States say Sunday's Crimean referendum was illegitimate and unconstitutional.

President Barack Obama told Russian President Vladimir Putin on Sunday that the vote "would never be recognized" by the United States, as he and other top U.S. officials warned Moscow against making further military moves toward southern and eastern Ukraine.

The EU is walking a tightrope between punishing Moscow and keeping open lines of communication with Russia for a diplomatic resolution of one of the worst geopolitical crises in years on its eastern doorstep.

Before Monday's meeting in Brussels, German Foreign Minister Frank-Walter Steinmeier said sanctions must leave "ways and possibilities open to prevent a further escalation that could lead to the division of Europe."

The EU has already suspended talks with Russia on a wide-ranging economic pact and a visa agreement. The bloc's leaders are meeting Thursday and Friday and could start slapping economic sanctions on Russia this weekend if Moscow does not back down.

Western allies are calling on Putin to "de-escalate" the crisis, support Ukrainian plans for political reform, return Russian troops in Crimea to their barracks and halt advances into Ukraine and military buildups along its borders.

Ukraine's new government in Kiev called Sunday's referendum a "circus" directed at gunpoint by Moscow. Putin, however, insisted it was conducted in "full accordance with international law and the U.N. charter" and cited Kosovo's independence from Serbia as its precedent.

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President Barack Obama is imposing sanctions against Russian officials after Crimea's vote to secede from Ukraine.

Obama's executive order issued Monday names seven Russian government officials. The United States also says it identifies and targets the assets of other individuals who aren't government officials but are supporting them.

The Treasury Department also is imposing sanctions on four Ukrainians, including former President Viktor Yanukovych and two Crimea-based separatist leaders.

The U.S. announcement came shortly after the European Union announced travel bans and asset freezes on 21 people.

The sanctions were expected after residents in Crimea voted overwhelmingly Sunday in favor of the split.