Donald Trump and Hillary Clinton win Arizona primaries

Washington, March 23  Republican and Democratic presidential frontrunners, Donald Trump and Hillary Clinton, cruised to big victories in the crucial Arizona primary even as they faced challenges from rivals in other nominating contests.

With his easy victory in Arizona's winner-take-all primary, Trump added another 58 delegates to his tally of 681 delegates, while closest rival, Texas Senator Ted Cruz with 425 delegates hoped to slow Trump's momentum with a victory Tuesday in the Utah caucuses.

A strong victory in Utah caucuses with more than 50 percent support would give Cruz all the state's 40 delegates and help him narrow the gap with Trump a little in the race for 1,237 delegates needed to win the Republican nomination.

Cruz is backed in Utah with its sizable Mormon population by the 2012 Republican nominee Mitt Romney, who backed Ohio Governor John Kasich in last week's Ohio primary.

Romney said he would vote for Cruz in Utah as part of an effort to deny Trump the nomination.

"The only path that remains to nominate a Republican rather than Mr. Trump is to have an open convention," he wrote in a posting on Facebook.

"At this stage, the only way we can reach an open convention is for Senator Cruz to be successful in as many of the remaining nominating elections as possible."

Kasich, who entered the day with 143 delegates handily won his home state last week despite a strong push by Trump. But that is Kasich's one and only victory and he seemed unlikely to add to his win total on Tuesday.

Heading into the polls in the shadow of a series of explosions in Brussels, killing at least 30 people, Trump reiterated his proposal for an open-ended ban on Muslims entering the US and for using extralegal means to fight terrorists.

Trump called for torturing Salah Abdeslam, a suspect in November's terrorist attack on Paris who was captured last week in Belgium.

"You know, he may be talking, but he'll talk a lot faster with torture," he told CNN.

Cruz responded to the attack with his own provocative proposal, calling for law enforcement authorities "to patrol and secure Muslim neighbourhoods before they become radicalised."

But Kasich was more restrained. "We are not at war with Islam; we're at war with radical Islam," he said.

Meanwhile, on the Democratic side, Clinton beat rival Bernie Sanders in the Arizona primary to take at least one of three Democratic presidential contests Tuesday in Western states.

Arizona was the biggest prize of the night, with 75 of the state's 85 delegates at stake based on the results of Tuesday's primary. Utah and Idaho also held caucuses Tuesday where a combined 56 delegates were on the line.

Speaking in San Diego after Clinton's projected win in Arizona, Sanders cited "record-breaking turnouts" in states that held contests Tuesday and said his campaign appealed to voters because "we are telling the truth."

"We cannot go forward as a nation unless we are prepared to confront the real issues facing our country,"