KIEV , Nov. 22 - Russia will be more aggressive towards Ukraine if the European Union does not honor a promise of visa-free travel for Ukrainians, Anders Fogh Rasmussen, the former NATO chief and now an adviser to Kiev 's president, said on Tuesday, Reuters reported.

Rasmussen said he hoped Ukraine would get a firm commitment at an EU-Ukraine summit on Thursday on waiving visas for Ukrainians making short visits to EU territory.

EU member states gave conditional approval to the move last week but agreed it would be implemented only after the bloc beefs up a mechanism to suspend visa-free deals in any emergency.

A mass influx of migrants last year made the EU warier of visa-free travel from outside the bloc and there are fears in Kiev , especially with France and Germany heading to elections next year in which anti-immigrant parties could surge, that the visa-free deal might be kicked into the long grass.

In addition, Donald Trump's election victory in the United States has Ukrainians worried that he might - based his warm rhetoric towards Russian President Vladimir Putin - look to mend U.S. relations with Russia at Kiev's expense.

Ukraine has been the heart of tensions between the West and Russia since Moscow annexed the Black Sea peninsula of Crimea in 2014 and went on to support separatist rebels in the east of the former Soviet republic.

"I do believe that, taking into account the uncertainty that has been created with the election of Trump, it's even more important that the EU demonstrates to Ukraine that EU policy is unchanged," Rasmussen told Reuters by phone.

"If on top of the uncertainty already created, you create new uncertainty because the EU does not deliver, then it could tempt Mr Putin to move further."

The EU and Washington imposed sanctions on Moscow over its role in the Ukraine conflict and have sought to develop closer ties with Kiev , though they have also grown annoyed with the slowness of Ukraine 's progress on reforms.

Rasmussen goes to Washington next week to meet members of Trump's transition team and Barack Obama's outgoing administration, where among other things he will lobby for Ukraine to receive defensive weaponry from the United States .

"If Russia succeeds in the aggression in Ukraine , it would definitely harm American interests overall," he said. "So that's why I will make the case in Washington that putting America 's interests first would also mean taking care of Ukrainian interests." (rt/ez)