PARIS, Oct 23 (Reuters) - Governments should open a new front in the international clampdown on tax evasion with a global minimum tax on billionaires, which could raise $250 billion annually, the EU Tax Observatory said on Monday.

If levied, the sum would be equivalent to only 2% of the nearly $13 trillion in wealth owned by the 2,700 billionaires globally, the research group hosted at the Paris School of Economics said.