KIEV (Reuters) - Ukrainian President Petro Poroshenko said on Monday Ukrainians risked becoming disillusioned with Ukraine's pro-European path if there are further delays to plans to cement its closer integration with the European Union.

The European Union reached an agreement on visa waivers for Ukraine in December, after weeks of stalling, but the decision has yet to come into effect.

"To delay further would be flagrantly unfair as Ukraine has paid a high price," Poroshenko told foreign ambassadors to Ukraine.

"It would also be dangerous because more unreasonable delays would undermine Ukrainians' faith in Europe, which in fact is what Russia is aiming for," he said, adding that Ukraine's EU association agreement also needed to be legally ratified.

Delays have raised criticism that the bloc was reneging on pledges to help Ukraine as it seeks to move away from Moscow's orbit in the wake of its 2013-14 pro-European uprising that ousted a Kremlin-backed president.

After the change in power, Russia annexed Ukraine's Crimea peninsula and is accused by Kiev and NATO of fuelling an ongoing pro-Russian separatist conflict in eastern Ukraine in which close to 10,000 people have been killed.

"We are all witnesses to efforts to build a new iron curtain and it is today's Russia that is building it," Poroshenko said.

His comments follow a final visit to Kiev by U.S. Vice President Joe Biden, who called for the international community to stand up to "coercion and aggression" from Russia.

Western support for Ukraine has contributed to a deterioration in relations with Russia to their worst since the Cold War.

Trump's open admiration of Russian President Vladimir Putin and stated desire to improve bilateral ties have stoked fears in Kiev that international resolve to hold Russia to account could waver.

(Reporting by Natalia Zinets; Writing by Alessandra Prentice)