US Republican presidential candidate Ted Cruz has won nominating contests in Kansas and Maine, denting frontrunner Donald Trump's momentum and bolstering Cruz's case that he is the best alternative for those bent on stopping the billionaire businessman.

On the Democratic side, frontrunner Hillary Clinton won in Louisiana, while her rival Bernie Sanders, a US senator from Vermont, won in Kansas and Nebraska.

Five states were holding nominating contests on Saturday as Trump and Clinton looked to strengthen their leads in the battle to pick nominees for the November 8 presidential election to succeed President Barack Obama.

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Trump won in Louisiana and Kentucky. The results were bad news for the remaining two Republican candidates, Marco Rubio, a US senator from Florida, and Ohio Governor John Kasich, who trailed in all four contests.

"The scream you hear, the howl that comes from Washington, DC, is utter terror at what 'We the People' are doing together," Cruz told supporters in Coeur d'Alene, Idaho, after his win in Kansas.

Cruz, a US senator from Texas who has promoted himself to voters as a true conservative, in contrast to Trump, also won a nonbinding "straw poll" of activists at the Conservative Political Action Conference near Washington.

"What we saw in Kansas is a manifestation of a real shift in momentum," Cruz told reporters in Idaho.

In the overall race for Republican delegates, Trump leads with at least 375 and Cruz has at least 291. Rubio has 123 delegates and Kasich has 33. It takes 1,237 delegates to win the Republican nomination for president.

The races on Saturday were open only to registered Republicans, excluding the independent and disaffected Democratic voters who have helped Trump's surge to the lead.

Even with his wins on Saturday, Sanders faces a tough task trying to make up the difference with Democratic frontrunner Clinton [Carlos Osorio/AP]

Al Jazeera's Gabriel Elizondo, reporting from Washington, DC, said that even though Cruz had made an apparent breakthrough, Trump had still won Louisiana, the largest state voting on Saturday.

Saturday's contests were the first since retired neurosurgeon Ben Carson dropped from the race, after polling in the single-digits in most of the nominating contests. Carson had drawn support from evangelical voters, a group that has also been a stronghold of Cruz.

Since winning seven of 11 contests on Super Tuesday, Trump has come under withering fire from a Republican establishment worried he will lead the party to a resounding defeat in November's election.

Mainstream Republicans have blanched at Trump's calls to build a wall on the border with Mexico, round up and deport 11 million undocumented immigrants, and temporarily bar all Muslims from entering the US.

Mitt Romney, the 2012 Republican presidential nominee, called Trump a phony and a fraud who was playing American voters for suckers, and 2008 nominee John McCain, a US senator from Arizona, said Trump's foreign policy views were uninformed and dangerous.

On the Democratic side, Clinton has opened up a big delegate lead and Sanders might have a tough time making up the difference. All states in the Democratic race award their delegates proportionally, meaning Clinton can keep piling up delegates even in states she loses.

Clinton has at least 1,117 delegates to Sanders' 477, including superdelegates - members of Congress, governors and party officials who can support the candidate of their choice. It takes 2,383 delegates to win the Democratic nomination.

The three states holding Democratic contests on Saturday had a total of 109 delegates at stake.

"Sanders might have rejuvenated his campaign after upsetting Clinton in two of the three states that voted, showing that while he trails Clinton in the delegate count needed to secure the nomination, he still has wide support," said Al Jazeera's Elizondo.

"In this most unpredictable election season, voters continue to surprise … sending a message that they are not ready for any candidate in either party to run away with the nomination just yet." 

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Source: Al Jazeera and agencies