BRUSSELS (Bloomberg) — The fight against tax havens by the Group of 20 advanced and emerging economies is already forcing targeted countries to cooperate, the European Union's tax commissioner said.

Monaco and Liechtenstein on March 26 joined a roster of states yielding to U.S. and European governments by revamping policies blamed for letting foreigners hide income from tax authorities. The changes add to moves by countries including Switzerland, Luxembourg and the Bahamas.

"Several jurisdictions have reacted to the new international pressure to indicate their new-found willingness to apply international standards of transparency and information exchange," EU Taxation and Customs Commissioner Laszlo Kovacs said in speech in Brussels yesterday. "We need to build on this and ensure that such declarations are transposed into action."

The comments show how the G-20 can already notch a success ahead of an April 2 summit in London, which plans to discuss opening up tax havens as well as tightening financial regulation and fighting a global recession.