WARSAW/BUDAPEST, Feb 24 (Reuters) – The countries on the European Union’s eastern flank, all NATO allies sharing borders with Ukraine except for the Czech Republic and Bulgaria, have also started preparations to receive potentially hundreds of thousands of people fleeing Ukraine.

“We must immediately respond to Russia’s criminal aggression on Ukraine. Europe and the free world has to stop Putin. Today’s European Council should approve fiercest possible sanctions,” Polish Prime Minister Morawiecki said.

The Polish government said it expects a decision on reinforcing NATO’s eastern flank after Russian forces invaded Ukraine, a government spokesman added.

Czech Prime Minister Petr Fiala said on Twitter that the Russian invasion of Ukraine was an “absolutely unjustifiable act of aggression toward and independent country, which cannot remain without reaction from EU and NATO.”

Czech Foreign Minister Jan Lipavsky added, also on Twitter: “Together with Allies, we will respond to this barbaric act of aggression.”

European Union leaders will discuss a further sanctions package on Russia at an emergency meeting later on Thursday, the EU said in a statement.

By early Thursday, Hungary had not yet explicitly condemned the attack, but its foreign minister said war was “the worst-case scenario.” He reiterated that Hungary fully supported Ukraine’s sovereignty and territorial integrity.

“The task now… is to guarantee the security of Hungarian people,” Foreign Minister Peter Szijjarto said on his official Facebook page. “Our embassy in Kyiv is operating, and ready to help Hungarians who are in the Ukraine right now.”

Romanian President Klaus Iohannis also condemned the Russia attack calling it a “very grave breach of international law, of Ukraine’s sovereignty and integrity.”

“I strongly condemn Russia’s military aggression against Ukraine. This act undermines the sovereignty and independence of Ukraine and constitutes a grave breach of international law,” Bulgarian Foreign Minister Teodora Genchovska said on Twitter.

(Reporting by bureaus across Central EuropeWriting by Krisztina ThanEditing by Peter Graff)