German IS sympathizers under surveillance

German Interior Minister Thomas de Maiziere told the "Bild am Sonntag" newspaper that security forces have received many tip-offs regarding possible attacks at Euro 2016, but added that there had been no concrete indications a terrorist attack was imminent during the tournament.

"There are officially some 500 threats that we have in our sights," he told the mass-market paper. "That is very extensive, but subject to change."

Germany has been on high alert for several months since the attacks last year in Paris and this year in Brussels. It's not known exactly how many German citizens are fighting or have fought in Syria or Iraq with IS, but estimates put the number in the hundreds.

Hooligans also being watched

The German interior minister added that homegrown hooligans were being closely watched.

German football hooligans have also been placed under observation by German and French police, and the two countries are cooperating closely on the issue of potential football violence, he said.

"We have set up an information exchange with France regarding German hooligans who are known to the police and who are violent and passed on the names and data of some 2,500 people," de Maiziere said.

De Maiziere said French authorities can work with that information during border controls, where they are being supported by German officers.

Only in their third day, the European Championships have been marred by violence between rival Russian and English fans in Marseille. Fights also broke out between locals and Northern Ireland supporters in Nice.

jbh/sms (dpa, AP)