Russia has kicked off weeklong celebrations marking the anniversary of Russia's annexation of Crimea, while the United States and the European Union reaffirmed their support for Ukraine's sovereignty and territorial integrity.

In a ceremony at the Moscow-backed legislature in Crimea on March 16, a choir sang the Russian national anthem.

The ceremony was shown live on Russian state television.

Russian President Vladimir Putin's envoy to Crimea, Oleg Belaventsev, congratulated State Council deputies on the first anniversary of Crimea's "return to Russia."

He handed certificates of honor to members of Crimea's Russian leadership and lawmakers for their "contribution to Crimea's reunification with Russia."

Belaventsev repeated Russia's claim that it moved to take control over Crimea because it feared for the people there following the ouster of Moscow-backed President Viktor Yanukovych in February 2014 after protests the Kremlin has cast as a U.S.-backed coup.

Russia annexed Crimea from Ukraine after sending troops there and staging a secession referendum on March 16, 2014, that was condemned by dozens of countries and declared illegal in an overwhelming vote in the UN General Assembly.

And Ukrainian government forces have been battling pro-Russian separatists in the country's east in a conflict that has killed more than 6,000 people since April.

Fighting has decreased since a cease-fire deal reached in Minsk on February 12, with both sides accusing each other of violations.

The United States and its European allies have imposed sanctions on Russia over its interference in Ukraine and support for the rebels.

The United States reiterated on March 16 that it won't recognize Russia's "attempted annexation."

In a statement, State Department spokeswoman Jen Psaki said that "sanctions related to Crimea will remain in place as long as the occupation continues."

"Over the last year, the human rights situation in Crimea has deteriorated dramatically, with mounting repression of minority communities and faiths, in particular Crimean Tatars, and systematic denial of fundamental freedoms," she added.

And in a meeting with Ukrainian Finance Minister Natalia Jaresko in Washington, Treasury Secretary Jack Lew said the United States would be ready to "increase the costs" to Russia if it failed to comply with the terms of the cease-fire agreement.

On March 16, the European Union reiterated that it will stick to its policy of not recognizing Russia's annexation of Crimea.

EU foreign-policy chief Federica Mogherini said in a statement that the 28-member bloc "does not recognize and continues to condemn this act of violation of international law."

She added that the EU "will remain committed to fully implement its nonrecognition policy, including through restrictive measures."

Mogherini also expressed concern over "the continuous military buildup and deterioration of the human rights situation in the Crimean Peninsula, including the denial of free speech and the persecution of persons belonging to minorities."

Germany also reiterated that it wouldn't recognize Russia's annexation of Crimea and accused Moscow of threatening peace in Europe.

Government spokesman Steffen Seibert told reporters on March 16 that Germany supports Ukraine "within its internationally recognized border" and he accused Moscow of threatening peace in Europe.

Seibert said Germany was also concerned about the worsening human rights situation in Crimea, where non-Russian minorities have been targeted.

He spoke before German Chancellor Angela Merkel met with Ukrainian President Petro Poroshenko in Berlin.

Following the talks, Poroshenko called on European leaders to make clear at a summit this week that they would impose further sanctions against Russia if Moscow did not implement the Minsk agreement.

"If the commitments are not fulfilled, and I really hope that on [March] 19 at the summit, that it will be said just as clearly, then the sanctions will continue to be imposed and will be stepped up," Poroshenko said.

Merkel said the sanctions against Russia must remain in place as long as the Minsk accord was not properly implemented.

She accused the separatists in eastern Ukraine of not fully complying with the agreement, saying, "There are considerable shortcomings in the separatists' compliance with the withdrawal of heavy weapons."

In Brussels, British Foreign Secretary Philip Hammond told reporters he hoped the EU "will have a clear political commitment to maintaining sanctions until Minsk has been delivered in its entirety."

"It is important to send a signal to the Russians that we are united, and that we are determined, and that they have to deliver on their commitments before they get sanctions relief," he added.

In an interview with several newspapers published on March 16, European Council President Donald Tusk called on EU leaders to maintain pressure on Russia with sanctions until the cease-fire deal is fully in place.

"I'm skeptical about the goodwill of the Russians and I'm convinced that what's needed is to maintain pressure," he was quoted as saying by Italian daily La Stampa.

With reporting by Reuters and dpa