People in Arizona give their views of the federal block on state immigration law
Arizona's governor says she will appeal against a federal court's decision to block parts of an anti-immigration law hours before it came into effect.
The court issued a temporary injunction against a requirement that police check the immigration status of suspects they had stopped while enforcing other laws.
A section making it a crime not to hold immigration papers was also blocked.
The ruling is seen as a warning to other states considering Arizona-style immigration strictures, analysts say.
The Arizona government's first step will be an appeal to the 9th Circuit Court of Appeals in San Francisco, but commentators are already predicting the legal battle could eventually go all the way to the Supreme Court.
Hispanic groups have called the Arizona's immigration law racist, but its defenders say it is a legitimate attempt to deal with the problem of illegal immigration.
Among the provisions kept was one making it illegal to transport and harbour illegal immigrants.
Also allowed to stand was a section of the law making it illegal for drivers to pick up day labourers from the street.
'Irreparable harm'
Republican Governor Jan Brewer, who signed the bill into law, called Wednesday's decision "a bump in the road", and vowed to launch an appeal.
"We will take a close look at every single element Judge [Susan] Bolton removed from the law, and we will soon file an expedited appeal at the United States Court of Appeals for the 9th Circuit," Ms Brewer said in a statement.
"This fight is far from over," she said, adding she was confident Arizona would win on appeal.
The Republican-controlled Arizona legislature passed the law in April, amid fears of rising crime caused by illegal aliens and complaints the federal government had failed to act on the matter.
The injunction is a temporary measure until the judge can decide on the law's constitutionality.
Polls suggested a majority of Americans favoured such measures and several other states were considering following Arizona-style strictures.
In the of the Arizona decision, those states will likely reconsider.
"Surely it's going to make states pause and consider how they're drafting legislation and how it fits in a constitutional framework," Dennis Burke, the US Attorney for Arizona, told The Associated Press.
"The proponents of this went into court saying there was no question that this was constitutional, and now you have a federal judge who's said 'hold on, there's major issues with this bill. So this idea that this is going to be a blueprint for other states is seriously in doubt."
In her decision, US District Judge Susan Bolton said the blocked sections of the law pre-empted the federal government's authority to set immigration law.
Among the controversial sections blocked by the judge was one making it a crime for undocumented workers to seek or apply for a job and another allowing police to arrest without a warrant people whom they had probable cause to believe had committed a crime for which they could be deported.
The US was likely to "suffer irreparable harm" if she did not block enforcement of those sections, she wrote.
"Requiring Arizona law enforcement officials and agencies to determine the immigration status of every person who is arrested burdens lawfully present aliens because their liberty will be restricted while their status is checked," she added.
She also wrote that the surge in requests for immigration status checks would force the federal government to shift resources away from its own priorities.
The judge also agreed with an argument by the administration of President Barack Obama that "the federal government has long rejected a system by which aliens' papers are routinely demanded and checked".
She let other parts of the law stand, including one barring Arizona counties and towns from restricting enforcement of federal immigration laws. These parts of the law come into effect on Thursday.
The US justice department hailed the ruling, while acknowledging "the frustration of Arizonans with the broken immigration system".
"A patchwork of state and local policies would seriously disrupt federal immigration enforcement and would ultimately be counterproductive," spokeswoman Hannah August said in a statement.
"We will continue to work toward smarter and more effective enforcement of our laws while pressing for a comprehensive approach that provides true security and strengthens accountability and responsibility in our immigration system at the national level."
The Mexican government, which has repeatedly expressed concerns about the Arizona law, called the ruling a "first step in the right direction".