Without offering specifics on any threats or suggestions on how to confront them, the leaders of the Senate and House intelligence committees on Sunday prodded the White House to work to prevent the Islamic State extremists from launching attacks on US soil.

The bipartisan pair of lawmakers shared a dire warning against the Islamic State group, which now has control of vast swaths of Syria and Iraq, has killed civilians from that region and beheaded American journalist James Foley.

"This is a group of people who are extraordinarily dangerous," said Sen Dianne Feinstein, the California Democrat who leads the Senate intelligence panel. "And they'll kill with abandon."

In a separate TV interview, the leader of the House Intelligence Committee warned that the leaders of the Islamic State, sometimes called ISIL or ISIS, are looking for a spectacular attack that would help them to raise money and recruit more fighters.

"ISIL would like to have a Western-style attack to continue this notion that they are the leading jihadist group in the world," said Republican Rep Mike Rogers.

The pair of lawmakers, who have access to some of the nation's most sensitive secrets and receive regular detailed briefings from the nation's spy agencies, offered dire predictions of an attack on the United States or its European allies if the militants are not confronted.

"They have announced that they don't intend to stop," Feinstein said. "They have announced that they will come after us if they can, that they will, quote, 'spill our blood.'"

The threat, Rogers said, could include Americans who have trained with Islamic State fighters. He said there are hundreds of Islamic State-trained Americans who can return to the US with their American passports.

Rogers said US intelligence agencies were tracking the Americans who are known to have travelled to the region. If they helped Islamic State fighters, he said, they should be charged under laws that prohibit Americans from aiding terrorists.

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