A top congressional Democrat and Republican both warned Sunday about more “lone wolf” attacks, inspired by Islamic jihad and easily promulgated through Internet propaganda.

"The police and the military have to be on guard," California Democratic Sen. Dianne Feinstein, chairwoman of the Senate Intelligence Committee, told CNN's "State of the Union.” "We need to think in some new ways."

Her warnings follow three such attacks last week.

On Wednesday, a Canadian soldier was killed when gunman Michael Zehaf-Bibeau stormed the county’s national war memorial and fatally shot a soldier, then entered the Canadian Parliament before being killed by police.

The attack in Ottawa came two days after a man described as being an Islamic State “inspired terrorist" ran over two soldiers in a parking lot in Quebec, killing one and injuring the other before being shot to death by police.

The man had been under surveillance by Canadian authorities, who feared he had jihadist ambitions and seized his passport when he tried to travel to Turkey.

Muslim leaders said Friday that Zehaf-Bibeau once complained that a Vancouver mosque he attended was too liberal and inclusive. They also said he was kicked out of the mosque after repeatedly spending the night there against officials’ wishes.

Zehaf-Bibeau’s motive remains unknown, but Canada Prime Minister Stephen Harper has called the shooting a terror attack. And the bloodshed has raised fears that Canada is suffering reprisals for joining the U.S.-led air campaign against Islamic State extremists in Iraq and Syria.

Zehaf-Bibeau, whose father was from Libya, was not being watched by authorities. But a top police official said he may have lashed out in frustration over delays in getting his passport.

On Thursday, Zale Thompson, a reclusive Muslim convert who ranted online against America, attacked two New York City police officers on a busy Queens street before being shot down by two uninjured officers.

Thompson has no clear ties to international extremists, and no motive has been established. But city police Commissioner William Bratton is calling the incident a terror attack.

Feinstein said Sunday that Internet propaganda and specific people are "really firing up this lone wolf phenomenon."

Concern over such attacks is nothing new but appears to be increasing.

Homeland Security Secretary Jeh Johnson has said in recent weeks that lone wolf attacks are now the country’s biggest domestic terror concern.

Such concern is in large part in response to the Islamic State’s aggressive, online propaganda campaign.

"You have to ferret it out,” Feinstein said. “You have to be able to watch it, and you have to be able to disrupt them."

She made her remarks the same day Texas GOP Rep. Michael McCaul, chairman of the House Homeland Security Committee, said the attacks showed the effectiveness of Islamic State’s Internet campaign. He also expressed concern about the difficulty is stopping the propaganda and reversing its effects.

"It's like finding a needle in a haystack, then getting (converts) out of that radicalization,” he said on ABC’s “This Week.”

McCaul described some of those radicalized over the Internet as people living in a basement and “very hard to stop."

The Associated Press contributed to this report.