PHOENIX, Arizona — A US federal court upheld the suspension of key parts of a controversial Arizona immigration law which came into force last year.

Arizona's governor slammed the ruling -- and vowed to appeal to the US Supreme Court if necessary -- but the Mexican government and rights groups welcomed the decision to maintain a freeze on the law's most disputed parts.

"It sends a very clear message, both to Arizona and to other states that might consider doing something like this, that this is an unconstitutional road to go down," said Omar Jadwat of the American Civil Liberties Union (ACLU).

"There were a lot of nails already in the coffin of this approach, but this is should be final blow," added the ACLU lawyer following the decision by the Ninth US Circuit Court of Appeals.

The disputed Arizona law took effect last July, but was stripped of a controversial provision that would have given police officers the power to check the immigration status of suspected criminals.

The provision had been blocked by a federal court that agreed with the US Department of Justice's argument that immigration issues are the jurisdiction of the US government -- not state governments.

Opponents said the law was xenophobic and would lead to people being stopped on the streets simply because of the way they look. The Mexican government issued a statement welcoming Monday's ruling.

But officials in Arizona say they have to act to stem a tide of illegal immigrants from across the border with Mexico, accompanied by soaring crime rates fueled by people smuggling and gun- and drug-running.

Arizona governor Jan Brewer slammed the ruling, calling it "internationalism run amok."

"I remain steadfast in my belief that Arizona and other states have a sovereign right and obligation to protect their citizens and enforce immigration law in accordance with federal statute," she said.

Arguing that the ruling "does harm to the safety and well-being of Arizonans who suffer the negative effects of illegal immigration," she added: "Today?s decision is internationalism run amok."

"It is outrageous that the Ninth Circuit Court would grant foreign nations the de facto right to veto the duly-enacted laws of a sovereign state of the United States,

And a statement by her office said she and Arizona Attorney General Tom Horne said they were considering their legal options.

"It has always been expected that this legal fight would be a long one. But the Ninth Circuit Court is the most overturned appeals court in the nation for a reason.

"Both Governor Brewer and Attorney General Horne believe that the constitutionality of (the law) will eventually be affirmed."

The row over the Arizona law has thrust the issue of the nation's estimated 11 million illegal immigrants once more into the spotlight, after a series of failed legislative attempts to bring them out of the shadows.

Opinion polls conducted before the law came into force found more than 60 percent of the US population supporting it.

One in three of the 6.6 million people in Arizona is foreign-born and an estimated 460,000 are illegal immigrants, most of whom are Mexican.