The Israel-Hamas war has heightened the threat of attacks in the United States, raising particular concerns for the Jewish and Muslim communities, FBI Director Christopher Wray warned Tuesday.

"We assess that the actions of Hamas and its allies will serve as an inspiration the likes of which we haven't seen since (the Islamic State group) launched its so-called caliphate several years ago," Wray told the Senate Committee on Homeland Security.

"It is a time to be concerned. We are in a dangerous period," he said. "This is not a time for panic, but it is a time for vigilance."

The Federal Bureau of Investigation chief said law enforcement "cannot and do not discount the possibility that Hamas or another foreign terrorist organization may exploit the current conflict to conduct attacks here on our own soil."

"Our most immediate concern is that violent extremists, individuals or small groups, will draw inspiration from the events of the Middle East and carry out attacks against Americans going about their daily lives," he said.

"That includes not just homegrown violent extremists inspired by a foreign terrorist organization but also domestic violent extremists targeting Jewish or Muslim communities."

Wray noted the arrest in Houston last week of a man who had been studying how to build bombs and posted online about "killing Jews" and the killing of a six-year-old Muslim boy in Illinois by his landlord, which is being investigated as a hate crime.

"The ongoing war in the Middle East has raised the threat of an attack against Americans in the United States to a whole 'nother level," Wray said.

Al-Qaeda, IS and Hezbollah have all called for attacks on US interests, Wray said, but the FBI is not "currently tracking an imminent credible threat from a foreign terrorist organization."

Threats to the Jewish community in the United States, however, are "reaching in some way sort of historic levels," the FBI director said.

"The reality is that the Jewish community is uniquely targeted by pretty much every terrorist organization across the spectrum," Wray said, adding that Jews make up just 2.4 percent of the American population but account for 60 percent of religious faith hate crimes.

'Very fine line to walk'

Christine Abizaid, director of the National Counterterrorism Center, told the Senate committee the United States is concerned by activity by Iran and Hezbollah in the Middle East "that could have significant escalatory consequences."

She said Iranian-aligned militant groups have conducted more than two dozen attacks against US forces in Iraq and Syria using rockets and unmanned aerial systems in addition to daily attacks on Israel by Lebanese Hezbollah.

"While these groups have the capability to conduct more sophisticated attacks than they have thus far demonstrated we assess Iran, Hezbollah and their linked proxies are trying to calibrate their activity, avoiding actions that would open up a concerted second front with the United States or Israel," Abizaid said.

"This is a very fine line to walk and in the present regional context their actions carry the potential for miscalculation, thus requiring heightened scrutiny in the region as we monitor for signs that the conflict could spread."