Police in Belgium and the Netherlands have arrested six suspected Islamic extremists in a sweep on a network thought to be planning attacks against U.S. targets in Europe.

Belgian authorities say they arrested two men belonging to a radical Islamic movement in Brussels Thursday and confiscated two Uzi machine pistols during a house search. A government spokesperson says the move followed a tip from Belgian security that one of the suspects might be preparing attacks against U.S. targets in Europe.

In the Netherlands, the Dutch prosecutors' office says four suspected Islamic extremists were arrested in Rotterdam Thursday night. Officials say passports and materials to make false credit cards were found during searches.

However, authorities in both countries say there is no apparent connection between those arrested and the devastating attacks in the United States earlier this week.

Meanwhile, Germany has released an airport worker held for 24 hours in connection with the attacks in New York and Washington. At the same time, German investigators are continuing a probe into Hamburg-based extremists allegedly involved in the attacks.

European leaders have vowed to do everything possible to track down and bring to justice those responsible for the attacks in New York and near Washington. In a statement, the European Union declared that organized terrorism will not be able to find refuge anywhere.