Joe Biden speaks at a press conference | Mark Wilson/Getty Images Joe Biden: Ukraine must reform or EU may lift Russia sanctions Kiev must ‘straighten up and fly right.’

Ukraine must make progress on promised economic and political reforms or the EU could backtrack on sanctions it imposed on Russia after the annexation of Ukraine’s Crimea peninsula in 2014, U.S. Vice President Joe Biden warned on Wednesday, Reuters reported.

“We know that if they give an excuse to the EU, there are at least five countries right now that want to say ‘We want out,'” Biden said to the Council on Foreign Relations in New York. Europeans could be tempted to say Ukraine was "owned by Russia anyway" before Petro Poroshenko became president, and decide to lift sanctions, he added.

The U.S. vice president met with President Poroshenko on Tuesday at the United Nations and called on Kiev to reform its justice and energy sectors, while acknowledging the country had met conditions for a third U.S. sovereign loan guarantee of up to $1 billion.

Biden said he told Poroshenko: "Everybody's willing to blame the victim, and you better straighten up and fly right."