Vice President Joe Biden on Tuesday reassured Ukrainian leaders that the U.S. stands with them in the face of Russian threats to their sovereignty, but urged Kiev to implement reforms to strengthen their country.

“You face very daunting problems, and some might say, humiliating threats,” Biden told members of Ukraine’s parliament. “But the opportunity to generate a united Ukraine, getting it right, is within your grasp. And we want to be your partner and friend in the project. We want to assist.”

Biden met with members of Ukraine’s parliament during a trip intended to show U.S. support for the embattled interim government in Kiev as pro-Russian militant groups press for autonomy in eastern Ukraine.

The vice president stressed the importance of upcoming elections and said they were an opportunity for Ukrainians to solidify their democracy.

“This is a second opportunity to make good on the promise of the Orange Revolution,” said Biden. “This is a genuine opportunity to get right all that happened the first time.”

“You have to fight the cancer of corruption that is endemic in your system right now,” he urged.

Biden’s visit comes as pro-Russian separatist groups refuse to back down in eastern Ukraine.

Ukraine, Russia, the U.S. and European Union negotiated a deal last week in Geneva that would see the pro-Russian groups who have seized land and government buildings stand down in exchange for amnesty. But those groups have said they are not bound by the negotiations and Russia on Tuesday accused Ukraine of not keeping the terms of the deal, further raising tensions.

The Obama administration has said that they are ready to impose further “costs” on Russia within days if they do not see clear steps to de-escalate the situation.

Russia has said that it has no intention of invading Ukraine after the Kremlin annexed Crimea, but Moscow has massed troops along the border between the two countries.

In his meeting with Ukrainian lawmakers, Biden praised them, saying that he did not “underestimate the incredible pressure you all are under.”

“Some of you are going to have to make some difficult personal decisions,” Biden said of the challenges ahead.