A U.S. congressional hearing on homegrown terrorism has been labelled "shameful" and "un-American" by prominent Muslim leaders.

A Republican-led Homeland Security committee began hearing testimony Thursday in Washington on radicalization in the U.S. Muslim community.

Analysis The CBC's Neil Macdonald in Washington writes on Singling Out Muslim Americans

Representative Peter King, the New York Republican who organized the hearing, has stirred controversy by accusing Muslims of refusing to help law enforcement with the growing number of terrorists and extremists.

"Let me make it clear today that I remain convinced that these hearings must go forward, and they will," King said.

"To back down would be a craven surrender to political correctness, and an abdication of what I believe to be the main responsibility of this committee — to protect America from a terrorist attack," he said. "Despite what passes for conventional wisdom in certain circles, there is nothing radical or 'unAmerican' in holding these hearings."

Democrat Sheila Jackson Lee said, "This hearing today is playing into al-Qaeda right now around the world," adding the committee was trampling on the U.S. Constitution.

Some critics have compared the hearing to overly zealous investigations of communism in the 1950s that led to false accusations that destroyed careers.

The hearing has reignited a debate in the United States over how to combat homegrown terrorism.

The Obama administration has tried to focus the discussion on radicalization in general, without singling out Muslims. But King admits he has singled out Muslims, and says al-Qaeda is the main threat to the U.S.

"This is al-Qaeda internationally. It is attempting to recruit within the United States," King told CBC News earlier Thursday. "People in this country are being self-radicalized."

Nagla Fetouh, a member of the Muslim organization My Faith, My Voice, fears the hearing will lead to "more hate, misunderstanding and discrimination against an already misrepresented community."

"Seven million Muslims deserve more than to be treated as guilty until proven innocent," Naeem Baig of the Islamic Circle of North America told CBC News.

King has been criticized by Muslim leaders and Democrats for pointing the finger at an entire religious community. When asked if they support King, members of his own party have either been lukewarm or mum on whether the hearing is appropriate.

On Sunday, a rally called "Today, I Am A Muslim, Too" was held in New York City to protest the targeting of American Muslims and Arabs.

"In the United States, we don’t practise guilt by association," said Denis McDonough, deputy national security adviser. "We will not stigmatize or demonize entire communities because of the actions of a few."

Security was stepped up around King on Thursday. He told media outlets the U.S. Capitol Police secured the hearing room in Congress and the surrounding area as well as his office. He has already been provided security by the New York Police Department and Nassau County police officers due to prior threats.

'Manipulated and lied to'

Witnesses at the hearing included family members of two young men who were inspired into terrorism, with deadly consequences. They testified that their relatives were brainwashed by radicals in the Muslim community.

Melvin Bledsoe, whose son is charged with killing an army private at a recruiting station in Little Rock, Ark., spoke about his son's conversion to Islam and his isolation from his family.

Bledsoe said he didn't fully understand what was happening as his son became increasingly distant, stopped coming home for holidays and changed his name. He said the U.S. is not being aggressive enough about rooting radical elements from the Islamic community.

The committee was also scheduled to hear from Abdirizak Bihi, the uncle of a young Somali-American who was recruited by the terrorist group al-Shabab and was killed shortly after returning to Somalia.

In his prepared remarks, Bihi said, "99.9 per cent of Muslim Somali-Americans are good citizens who are very grateful for the opportunities they have and are very busy in chasing their American dream."

King contends Muslims should not feel threatened by the hearings.

"If there is going to be animosity, I would blame it on my opponents," he said Wednesday in a nationally broadcast interview.

Director of national intelligence James Clapper was also scheduled to address the threat of homegrown terrorism Thursday. He was expected to tell the media that 2010 saw more plots involving homegrown Sunni Muslim extremists ideologically aligned with al-Qaeda than in the previous year.

"Key to this trend has been the development of a U.S.-specific narrative that motivates individuals to violence," Clapper's prepared remarks said.