Members of the European Parliament have denounced Russia’s actions in Crimes as an “invasion”.

MEPs also said this Sunday’s referendum on whether to split from Ukraine and join Russia was a “clear breach” of international law.

José Ignacio Salafranca-Sanchez-Neyra, a centre-right MEP from Spain, said: “Russia has to understand that the price of this operation, if she insist this is the aim, it will be a serious international isolation, the EU will take measures very restrictive”

Delegations from Russia and Ukraine were both in Strasbourg for talks with senior lawmakers.

Petro Poroshenko, a Ukrainian MP widely tipped to join the race to become the next president of Ukraine, said that the government in Kiev is willing to negotiate on some areas.

“This is nothing against Russia, this is just to stop the aggression. We are ready for any compromise, we are ready for compromise for languages, for rights of autonomy, for the status of Sebarstopol. The only thing we are not ready to have any compromise is the territorial integrity of my country,” he told euronews.

A top Russian parliamentarian representing Vladimir Putin argued the EU would be wrong to slap sanctions on senior officials in Moscow.

Alexey Pushkov, chairman of the Duma’s Foreign Affairs Committee, said: “We acknowledged very serious disagreements (with MEPs) in assessments of the situation in the Ukraine. However we came to the conclusion that it’s better to minimize the damage which could occur in this situation because it’s neither in in the interest of Russia nor of the EU: that’s where we agreed.”

EU foreign ministers meet on Monday to approve which Russian officials will face measures such as visa bans and asset freezes.