John Bacon

USA TODAY

Ukrainian Prime Minister Arseniy Yatsenyuk resigned Sunday under pressure to expedite reforms in the former Soviet-bloc nation.

Yatsenyuk's government has been besieged by war, corruption and economic struggles. His cabinet survived a no-confidence vote in February, but two parties left the governing coalition in protest that the prime minister wasn't ousted, a move that deprived the coalition of a majority in parliament.

President Petro Poroshenko said then that Yatsenyuk had lost support and should resign. Public opinion polls have showed support for Yatsenyuk as low as 1%.

Yatsenyuk, who will formally leave the post Tuesday, said the political crisis was "artificial." He said too much emphasis had been put on getting him out of office instead of making necessary changes. Parliament speaker Volodymyr Groysman was nominated to assume the prime minister post, Yatsenyuk said.

"I thank our nation, society, civil society activists, volunteers; I thank each and every one of you for your endurance and patience," Yatsenyuk said in a statement he also tweeted. "As of today my goals are broader: new electoral law, constitutional reform, judicial reform, Ukraine’s membership in the EU and NATO."

Yatsenyuk was an opposition leader in 2014 when massive protests helped drive pro-Russia President Viktor Yanukovych from power. Yanukovych had been viewed as slowing Ukraine's economic march toward the West. But his resignation sparked an outcry from Moscow, and within weeks Russia annexed Crimea.

A violent pro-Moscow insurgency ensued, compounding Ukraine's economic struggles. In eastern Ukraine, government forces have faced fierce assaults from militants despite a shaky cease-fire deal that took hold in September.

Ukrainian leaders have implemented some economic and political changes. Ukraine created a more professional national police force, closed some banks linked to money laundering and cut subsidies for gas and electric service.

The changes did little to curb the economic hardships or to satisfy reformists and European investors. In the United States, the Obama administration had expressed support for $1 billion in loan guarantees once a new government was formed.

On Sunday, Vice President Biden called Yatsenyuk to thank him for his efforts "during a historic time for Ukraine," the White House said in a statement. Biden and Yatsenyuk agreed on the importance of assembling a new cabinet committed to reforms recommended by the International Monetary Fund and European Union, the statement said.

Contributing: Oren Dorell