A New York Republican has pressed ahead with congressional hearings on the threat of homegrown Islamist terrorism , dismissing claims of a McCarthyite witch-hunt against America's Muslims.

Peter King, who chairs the homeland security committee in the House of Representatives, said the hearings were essential to national security, and that Muslim leaders should do more to help authorities prevent extremist attacks.

"The main goal is to show the extent of radicalisation within the Muslim-American community, how dangerous that is, how serious that is," he told Fox television. "It's a real threat. It's a growing threat, and it's not just me saying this."

He accused community leaders of not doing enough to protect America from attacks – although he said the majority of US Muslims were "good Americans".

"The fact is, the main threat is coming from within the Muslim community," he said. "The Muslim community should be embracing what I am doing, should be willing to co-operate because they should be trying to root these people out of their community and co-operate with the police and the FBI."

King's focus on extremists in the Muslim community – to the exclusion of other potential threats – has outraged security experts and human rights activists.

The Congressman has rejected calls from Democrats on the committee to broaden the hearings to look at threats from white supremacists and anti-tax protesters – both of whom have carried out fatal attacks in recent months.

Several hundred protesters, led by imams, rabbis and priests, met in Times Square on Sunday to denounce King.

In the Monday's Washington Post, John Esposito, a professor of Islamic Studies at Georgetown University, called the hearings an excuse for "Islamaphobia draped in the American flag".

He criticised King for not calling security experts to the hearing, and noted that federal government officials had acknowledged they had several times received important information from the Muslim community that prevented attacks.

Esposito went on: "Peter King's hearing is a staged event that will do little to shed light on the causes of domestic terrorism. If that were the goal then why not have government and non-government experts testify? Instead the hearing will be a platform for Islamophobia draped in the American flag, reinforcing ignorance, stereotypes, bigotry and intolerance in the name of national security."

The White House also responded to the controversy, sending the deputy national security advisor, Denis McDonough, to a mosque in the Virginia suburbs of Washington on Sunday. He told an interfaith service that no group should bear sole responsibility for extremism.

McDonough said: "No one community can be expected to become experts in terrorist organisations, how they are evolving, how they are using new tools and technology to reach our young people."

Two of the witnesses scheduled to testify at the hearing are relatives of men who were recruited by extremists. One is the uncle of a Somali man from Minneapolis, who is believed to have been killed in Somalia. Another is the father of Carlos Bledsoe, a convert to Islam accused of killing a soldier at a military recruiment centre in Arkansas in 2009.

A third, Zuhdi Jasser, a navy veteran and doctor, is well-connected to the Republican party and has made two films warning of the dangers of radical jihad in America.

Keith Ellison, a Minnesota Democrat and the first Muslim elected to Congress, is scheduled to testify at the hearings, which he has branded "McCarthyite".

He told the Minneapolis Star Tribune: "Its a bad idea to single out a religious minority group for an investigative hearing on violent radicalisation.

"I think it would be a problem to say we are going to have an investigation congressional hearing on Irish people who drink too much, or black people who sell drugs, or Jewish people who are engaged in financial crimes, or white people who commit bias crimes. Clearly this is singling out a particular group."

King told Fox television that the witnesses would provide much-needed information about how extremist organisations gained recruits in America. He repeated his charge of non-co-operation from Muslims, saying: "Somehow a wall of silence has developed."