The former prime minister of Ukraine says the EU must unite and convince Russia that it truly exists.
Yulia Tymoshenko says Russia must understand that the Ukraine is a full and independent state, and not just a region.
Speaking at the European People's Party (EPP) congress in Dublin, Ms Tymoshenko said Europe could not stand by and watch its largest country "be torn to shreds".
Speaking through an interpreter, she said allowing a referendum on Crimea would threaten the stability of all of Europe:
Her comments come as Ukraine has warned its armed forces will act if Russia moves any further into its territory. This afternoon, MPs in the Crimea region have voted to make it part of Russia which Kiev says is 'illegitimate'.
Around 100 people from various Eastern European countries have attended an anti-Russian demonstration in Dublin, as European leaders for a two-day summit.
Ukrainian opposition leader Vitali Klitschko says the very independence of Ukraine is at stake.
The former heavyweight boxing world champion has previously said he will run for the Presidency of Ukraine. Klitschko, also known as "Dr. Ironfist", told journalists in parliament "I will be on the ballot". Mr. Klitschko arrived at a Ukraine rally in Dublin earlier:
There is a heavy security operation is in place in Dublin for the major gathering of European leaders.
Up to 2,000 people from across Europe are expected at the Convention Centre for the congress of the European People's Party (EPP). Major European Union leaders including Jose-Manuel Barroso and Angela Merkel are due at the event later.
It is taking place at the Convention Centre in Dublin
Local traffic restrictions are in place for the next two days.
During the event the EPP - of which Fine Gael is a member - will launch its EU-wide campaign for the European elections in May. Around 2,000 participants are expected to attend the congress.
It will also select the EPP candidate for the election of the President of the European Commission.
Several names have been mentioned as possible contenders for the EPP nomination including Jean-Claude Junker - a former Prime Minister of Luxembourg - and the former Latvian leader, Valdis Dombrovskis.
