BRUSSELS (Reuters) - The European Union agreed on Tuesday to freeze assets of Islamist militants and their financial backers even if they are not on U.N. blacklists, an initiative advanced by France after deadly attacks in Paris, Brussels and Nice.

Until now, EU rules allowed only for sanctions on individuals and companies targeted by the United Nations. EU governments could act individually. There was no EU-wide policy.

No one was put under sanctions on Tuesday, but the new rules will allow the EU to target militants who have planned or taken part in attacks, as well as those who finance or arm militant groups such as Islamic State and al Qaeda, and those who seek to recruit more members.

Foreign nationals suspected of fighting for or supporting Islamist militants in Syria and Iraq will also now be put under Europe-wide travel bans, barring them from entry to the bloc.

EU nationals will also be hit with asset freezes, although they cannot be blocked from returning home and governments have promised to arrest and prosecute them.

French, German, Belgian and British citizens have joined insurgent forces in Syria and Iraq and some returning volunteers took part in the November attacks in Paris and those in Brussels in March. Islamic State claimed responsibility for those as well as the attack in Nice in July.

"Such measures will target particularly the so-called foreign fighters," the European Council of EU governments said in a statement. "The EU will be able to list any person who meets the criteria, including EU nationals who have supported these organizations outside the EU and who then return."

While the number of European foreign fighters is difficult to track, a Dutch study showed in April that more than 4,200 Europeans had gone to fight in Syria's civil war, of whom 30 percent had since returned and 14 percent were confirmed dead.

(Reporting by Robin Emmott; editing by Mark Heinrich)