The terrorism threat against the United States is increasing and Americans are not as safe as they were a year or two ago, the leaders of the House and Senate intelligence committees said on Sunday.

Senator Dianne Feinstein and Representative Mike Rogers appeared together on CNN's State of the Union, on the day that al-Qaida's US spokesperson called for attacks on US interests around the world. Rogers said al-Qaida groups had changed their means of communication as a result of leaks about US surveillance programs, making it harder to detect potential plots in the early planning stages.

"We're fighting amongst ourselves here in this country about the role of our intelligence community that it is having an impact on our ability to stop what is a growing number of threats," he said. "And so we've got to shake ourselves out of this pretty soon and understand that our intelligence services are not the bad guys."

Feinstein, a California Democrat, said there were more terrorist groups than ever, with more sophisticated and hard-to-detect bombs. She said: "There is huge malevolence out there."

Rogers, a Republican from Michigan, said there was enormous pressure on US intelligence services "to get it right, to prevent an attack" and said that job was getting more difficult because al-Qaida is changing, with more affiliates around the world. He said groups that once operated independently had now joined with al-Qaida.

Rogers also said terrorists were adopting the idea that "maybe smaller events are OK" and still might achieve their goals. "That makes it exponentially harder for our intelligence services to stop an event like that from happening," he said.

House intelligence committee chairman Mike Rogers said terrorists now thought 'maybe smaller events are OK'. Photograph: J Scott Applewhite/AP

Although neither lawmaker offered specifics about what led them to their conclusions, Feinstein spoke generally of "a real displaced aggression in this very fundamentalist jihadist Islamic community, and that is that the West is responsible for everything that goes wrong and that the only thing that's going to solve this is Islamic sharia law and the concept of the caliphate".