US Republican presidential candidates strained to take advantage of Donald Trump's absence in Thursday's presidential debate, mocking the frontrunner for boycotting the last contest before voting begins.

Trump withdrew from the final debate in Des Moines, Iowa, in a row with Fox News after the broadcaster refused to drop host Megyn Kelly, whom he accused of unfair treatment.

Texas Senator Ted Cruz, who is locked in a tight contest with Trump in Iowa, opened the event with a sarcastic impression of the real estate mogul's frequent insults of his opponents.

"I'm a maniac and everyone on this stage is stupid, fat and ugly, and Ben, you're a terrible surgeon," Cruz told his rivals, including Ben Carson, a retired neurosurgeon. "Now that we've gotten the Donald Trump portion out of the way," he continued.

READ MORE: Republican frontrunners clash in tense US debate

Former Florida Governor Jeb Bush, a frequent target of Trump, said with a wry smile: "I kind of miss Donald Trump; he was a teddy bear to me."

Live coverage

Instead of attending the debate, Trump held a competing rally also in Des Moines, an event that his campaign said was raising money for military veterans. 

"When you're treated badly, you have to stick up for your rights," Trump said, explaining he was skipping the debate because he felt Fox News had dealt with him unfairly.

He added: "We have to stick up for ourselves as people and we have to stick up for our country if we're being mistreated."

Reporting from Iowa, Al Jazeera's Alan Fisher said Trump's move appeared to pay off, as his event drew extensive live TV coverage and helped him reach as many people as he would have done with the Fox debate. 

"On one channel we have the main contenders talking about how they would be good presidents and appealing for the votes of the people in Iowa; on all the other channels, we have the leading contender saying the reason I boycotted is that I don't like to treated badly," he said.

"It will go down very well with the Donald Trump supporters."

READ MORE: Trump ducks out of debate as Iowa caucus beckons

Ryan Grim, the Washington Bureau chief of The Huffington Post, told Al Jazeera: "The Republican debate without Trump on stage lacked a lot of the energy of the previous ones.  

"And I think you are going to see, when the ratings come out tomorrow, that fewer people watched this one and more people collectively watched Donald Trump.

"He did not get pushed around by anyone else while his opponents got smashed by each other." he said.

Debate highlights

Trump's absence put the spotlight on Cruz, who is challenging for the lead in Iowa, as well as on Florida Senator Marco Rubio, who needs a strong showing in the state to stay competitive.

The two senators engaged in a lengthy debate on immigration. Both have been accused of shifting their stances on legalising some of those in the US illegally, a position opposed by many GOP voters.

Rubio pledged that as president he would go after "terrorists" and shut down mosques in the US if there were indications that the Muslim religious centres were being used to radicalise people.

READ MORE: Trump is a symptom not the disease

Kentucky Senator Rand Paul raised concerns about the US getting involved militarily in Syria.

The candidates largely sidestepped direct confrontations with each other, focusing some of their most pointed attacks on Democratic frontrunner Hillary Clinton.

Voters in Iowa will head to the polls on Monday to pick their parties' presidential nominees for the 2016 campaign. 

Source: Al Jazeera And AP