French Foreign Minister Laurent Fabius said Sunday that Crimea's referendum to decide whether the autonomous republic will break away from Ukraine is "illegal" and "contrary to Ukrainian Constitution", according to a Foreign Ministry statement.

As one of the five permanent members of the UN Security Counsil, "Russia has particular responsibilities on the international scene," and "must recognize and respect the sovereignty and territorial integrity of Ukraine," the French top diplomat said in the declaration.

France urges Russia to immediately take measures to avoid a "useless" and "dangerous" escalation of Ukrainian crisis, he added.

Some 1,200 polling stations opened Sunday in Crimea for a referendum to decide whether it should break away from Ukraine to join Russia.

The final results of the referendum will not be announced until Monday. Local television quoted late Sunday an exit poll by the Crimean Republic Institute for Political and Social Studies as saying that 93 percent of voters were in favor of joining Russia.