WASHINGTON (AFP) — The United States and Europe targeted Vladimir Putin’s inner circle on Monday, slapping sanctions on senior officials to pressure the Kremlin to abandon moves to annex Crimea.

The move came after the breakaway Ukrainian region voted to join Russia, in a referendum Kiev and the West deems illegitimate — and embarked on the next steps to formally embrace Kremlin rule.

“We have been guided by a fundamental principle,” US President Barack Obama said at the White House, a day after his latest call to his Russian counterpart Putin fell on deaf ears.

“The future of Ukraine must be decided by the people of Ukraine. That means Ukraine’s sovereignty and territorial integrity must be respected and international law must be upheld.”

The coordinated measures will freeze assets of key Russian presidential aides and lawmakers and target Crimean “separatist” leaders and ousted former Ukrainian president Viktor Yanukovcych.

“If Russia continues to interfere in Ukraine, we stand ready to impose further sanctions,” Obama warned, announcing that Vice President Joe Biden would head to Europe to coordinate with allies.

Obama said a diplomatic solution to the crisis was still possible if Russia pulls its troops back to barracks in Crimea, allows foreign observers to deploy and agrees to negotiate with Ukraine.

But he warned: “Further provocations will just further isolate Russia and diminish their place in the world.”

US officials said the moves were intended to strike at “cronies” around Russia’s President Putin, and to impose a heavy cost for the Crimean referendum and the arrival of Kremlin forces.

“These are clearly people who are very close to President Putin,” said one US official on condition of anonymity.

The official noted, however, that the government had not taken what would have been the “extraordinary” step of personally sanctioning Putin as a foreign head of state.

Another senior American official added: “These are by far the most comprehensive sanctions applied to Russia since the end of the Cold War, far and away.”

European Union Foreign Ministers on Monday unveiled travel bans and asset freezes against 13 Russian officials and eight Ukrainian officials from Crimea.

It did not identify those targeted, but US officials said the EU list would be announced publicly on Tuesday and contained some overlap with its own measures.

Lithuanian Foreign Minister Linas Linkevicius tweeted that there would be “more EU measures in (a) few days.”

Obama, who spoke to Putin on Sunday, unveiled a new executive order, naming seven key Russian officials and four more from Ukraine and Crimea.

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

They will not be allowed to do business with Americans and will find it difficult to make financial transactions using dollars.

The high profile list of Putin acolytes includes Deputy Prime Minister Dmitry Rogozin who has branded US support for interim anti-Moscow Ukrainian leaders as a “circus.”

The US and EU moves came a day after Crimea voted in a referendum, which US officials described as deeply flawed and marked by irregularities, for Kremlin rule.

In Washington, senior officials said the list of those sanctioned also included Vladislav Surkov and Sergei Glazyev, key aides to Putin and Duma members Leonid Slutsky, Yelena Mizulina.

Federation Council members Andrei Klishas and Valentina Matviyenko are also targeted.

The officials targeted in Crimea include Sergei Aksyonov, who has named himself the interim prime minister of the territory, and Vladimir Konstantinov, the speaker of the Crimean parliament.

Any assets of Yanukovych and Viktor Medvedchuk, leader of the pro-Russia “Ukrainian Choice” faction, in the United States will also be seized, the White House said.