The Obama administration yesterday sued Arizona over the state's strict new immigration law in a move that drew fire from Republicans, who said the border needed more security.

The Arizona law requires state and local police to investigate the immigration status of anyone they reasonably suspect of being an illegal immigrant, provoking criticism that it is unconstitutional and would sap law enforcement resources.

The Republican-controlled Arizona legislature passed the law to try to stem the flood of thousands of illegal immigrants who cross its border from Mexico each month, and to cut down on drug trafficking and other crimes in the area.

The lawsuit is part of a broader approach by Barack Obama to deal with the 10.8 million illegal immigrants believed to be in the country. But the legal action is a political gamble by the administration, as a Pew Research Centre poll showed 59 per cent of people approve of the Arizona crackdown.

The Arizona law would "interfere with vital foreign policy and national security interests by disrupting the United States' relationship with Mexico and other countries", said the Justice Department, which filed the lawsuit in a federal court in Arizona, asking for a preliminary and permanent injunction.

Mexico and several civil liberties groups have opposed the Arizona measure, and several other legal challenges are pending.