A US lawmaker on Thursday was to hold provocative hearings on the alleged radicalization of US Muslims, in a move critics say fans anti-Islam sentiment nearly a decade after the 9/11 attacks.

Representative Peter King, the Republican who chairs the House Homeland Security Committee, has promised a thorough probe, setting the stage for one of the most controversial congressional debates since the 2001 attacks.

“I want (Americans) to realize the extent to which Al-Qaeda is attempting to radicalize within the Muslim-American community,” King said Wednesday in summing up his intent.

The nation’s major Muslim groups — none of which have been invited to testify at the Capitol Hill hearing — and other rights defenders have blasted King’s “fear-mongering.”

“The seven million Americans (who are Muslim)… deserve more than collective guilt by suspicion,” said Shahid Buttar, who heads the non-denominational and non-partisan Bill of Rights Defense Committee.

By trafficking in bias and xenophobia, “Representative King aims to essentially be the (Joseph) McCarthy of the 21st century,” Buttar said.

McCarthyism refers to allegations of treason or subversion without proof, and was coined after the former US senator’s anti-communist witch-hunts in the 1940s and 50s.

King has said that Muslim leaders and mosque imams are doing too little to stop the radicalization of young Americans and are not cooperating with law enforcement. He has also said most US mosques are controlled by extremists.

The charges have alarmed US Muslim communities — the very ones President Barack Obama’s administration insists have been crucial to helping reduce the extremist threat.

Obama’s Attorney General Eric Holder shot down King’s assessment that Muslim leaders have not helped law enforcement, stressing that they “have contributed significantly” to thwarting attacks.

“We don’t want to stigmatize, we don’t want to alienate entire communities,” Holder said.

Imam Johari Abdul-Malik of the Coordinating Council of Muslim Organizations insisted that King was launching a modern-day “witch-hunt.”

But he and others acknowledged that some American Muslims, while the numbers are small, had indeed been radicalized in the United States.

“We’re not in denial as a community that something is going on,” he said.

King is “on to something, but he’s moving in the wrong direction,” he said, voicing the same frustration held by many Muslim leaders, who say they are still viewed with suspicion despite the help they provide to law enforcement.

The Council on American-Islamic Relations expressed concern with how King “has been singling out and stigmatizing the American Muslim community.”

CAIR director Nihad Awad warned that King’s “approach is going to radicalize young people.”

Several rights groups, including the American Civil Liberties Union, insist the probe should be broadened to include all extremist violence — though not extremist thought, which they insist is protected by the US Constitution.

With the battle lines drawn, the congressman at the center of the storm has vowed he “will not back down” on his investigation, which has divided fellow lawmakers.

House Majority Leader Eric Cantor on Tuesday reiterated his support for the hearings, but fellow Republican and House Speaker John Boehner has been mute on the issue, essentially distancing himself from King.

Democratic Senate Majority Leader Harry Reid said he was “deeply concerned about these hearings, which demonize law-abiding American Muslims who make important contributions to our society.”

House Democratic Whip Steny Hoyer has also objected to the hearing, saying it “sends the wrong message to the Muslim-American community.”

“We need them to work with law enforcement to identify terrorist threats, not be afraid of them,” he said in a statement.

King said two Muslim-Americans with knowledge of radicalization practices in US mosques will testify, as well as an African-American whose son was radicalized and converted to Islam.

Representative Keith Ellison, the first Muslim elected to the US Congress, has said he would appear before the committee, in part to offer “an alternative view” to King’s.

CAIR cited a recent study by Duke University that said 11 Muslim Americans have committed domestic terror attacks since 9/11, killing 33 people, compared to about 150,000 murders in the country over the same period.