The US Homeland Security secretary said Wednesday that Washington fears Europe may be a staging ground for terrorist attacks on the United States. Michael Chertoff said in an interview with British Broadcasting Corp. radio that his fears were based on how easy it is for Europeans to travel to the United Sates. He said there was also evidence of homegrown terrorism in European countries. "One of the things we've become concerned about lately is the possibility of Europe becoming a platform for a threat against the United States," Chertoff said. Washington has no plans to start asking Europeans to apply for visas to travel to the United States but they could be required to register online before traveling, Chertoff said.