The existence of such a search programme was disclosed on Thursday by US News and World Report's website.
The report said the US government had a secret programme monitoring homes and workplaces of Muslims and mosques in at least six cities for signs of nuclear radiation.
Up to 120 Muslim sites in the Washington area, and more in New York, Chicago, Seattle, Detroit and Las Vegas, have been regularly monitored for radiation for more than three years over concerns about nuclear terrorism after the 11 September 2001 attacks, the publication reported.
The Times reported on Saturday: "Government agencies (had) disclosed that they have installed radiation-detection equipment at ports, subway stations and other public locations, but extensive surreptitious monitoring of private property has not been publicly known."
The newspaper said the US federal government had given thousands of radiation alarms, worn like mobile phones on the belt, to police and fire departments in major cities.
"Surreptitious monitoring of private property has not been publicly known"
The New York Times
It quoted Brian Roehrkasse, a spokesman for the justice department, confirming that law enforcement personnel were conducting "passive operations in publicly accessible areas to detect the presence of radiological materials, in a manner that protects US constitutional rights".
The administration of George Bush, the US president, has been criticised over revelations that government agencies - including the National Security Agency, the Department of Defence, and the FBI - spied on US citizens without first obtaining court orders as mandated by law.
Bush, who authorised the NSA surveillance, maintains that the spying is legal and that he has the legal authority to permit such activities.
"All Americans should be concerned about the apparent trend toward a two-tiered system of justice, with full rights for most citizens, and another diminished set of rights for Muslims"
Council on American-Islamic Relations (CAIR) statement
The Council on American-Islamic Relations (CAIR) advocacy group said the report, coupled with news of the domestic eavesdropping, "could lead to the perception that we are no longer a nation ruled by law, but instead one in which fear trumps constitutional rights.
"All Americans should be concerned about the apparent trend toward a two-tiered system of justice, with full rights for most citizens, and another diminished set of rights for Muslims," it said in a statement.
Established in 1994, CAIR is America's largest Islamic civil liberties group, with regional offices nationwide and in Canada. The national headquarters is in Washington DC.