LONDON (AP) -- Homeland Security Secretary Michael Chertoff says there are fears that Europe could become a staging ground for terror attacks on the U.S.

In an interview with the BBC, Chertoff says he's concerned about how easy it is for Europeans to enter the U.S.

Chertoff says most European tourists don't need a visa to visit the states, giving officials a "very small window of opportunity" to check them out.

He says Washington has no plans to start requiring visas for European visitors, but they could be required to register online before they travel.

Chertoff also notes evidence of homegrown terrorism European countries, citing such attacks at the 2004 train bombings in Madrid and the 2005 subway bombing in London.

He says there's a "certain sense of complacency" about terrorism in the U.S., but that incidents in Europe show that terrorism isn't going away.