Crimea's referendum to join Russia was "illegal", an advisory body of the pro-democracy Council of Europe said Friday as East-West tensions mounted over Moscow's annexation of the Ukrainian peninsula.
The Council of Europe's so-called Venice Commission which is made up of independent constitutional experts said Crimea's vote to secede was undemocratic and violated Ukraine's constitution.
"The Constitution of Ukraine... provides for the indivisibility of the country and does not allow the holding of any local referendum on secession from Ukraine," said the commission in a statement.
"Only a consultative referendum on increased autonomy could be permissible under the Ukrainian Constitution."
World leaders have refused to recognizee Crimea's secession poll held over the weekend in which 96 percent of voters in the Black Sea peninsula rejected the new pro-European government in Kiev and voted instead to join Russia.
The West has blacklisted 33 Russian politicians, members of President Vladimir Putin's inner circle, and Black Sea and Crimea commanders in retaliation after Moscow on Tuesday signed a treaty to absorb Crimea into its territory.
Europe on Friday signed the political section of a landmark treaty on closer ties with Kiev's new pro-EU government.
A plenary session of the Venice Commission confirmed an earlier opinion that the referendum was not "held in line with European democratic standards".
"Any referendum on the status of a territory should have been preceded by serious negotiations among all stakeholders. Such negotiations did not take place," said the statement.
Russia's representative at the commission, Taliya Khabrieva, said many countries had seceded through local referendums, pointing to Eritrea, Bangladesh, and more closer to home, Kosovo.
"A large number of new states emerged after exercising this right," she said.
Ukraine joined the Strasbourg-based Council of Europe, a body created to protect human rights, democracy and the rule of law, in 1995 and Russia a year later.