Republican presidential frontrunner Donald Trump was endorsed by former Republican vice- presidential candidate Sarah Palin in a move which could raise his standing among female voters and conservatives less than two weeks before the Iowa caucus.

"I am proud to endorse Donald J Trump for president," Palin said in a statement provided by Trump's campaign to NBC News. The former Alaska governor made the endorsement formal on Tuesday (19 January) during a campaign stop in Iowa, the New York Times reported.

Palin joined Trump during a campaign rally at Iowa State University, where she spoke of her ardent support for the GOP candidate. "Are you ready for the leader to make America great again?" she said. "Are you ready to stump for Trump? I'm here to support the next president of the United States—Donald Trump."

According to the New York Times, Palin's support is the highest-profile backing for a Republican contender thus far. It also comes on the day that Iowa's Governor Terry Branstad, a Republican, said he hopes Texas Senator Ted Cruz is defeated in Iowa. Cruz has steadily risen in the polls and is even leading Trump in Iowa.

"He's been going rogue left and right," Palin said of Trump. "That's why he's doing so well. He's been able to tear the veil off of this idea of the system."

Craig Robinson, the former political director of the Republican Party of Iowa, told the newspaper that Palin could be especially helpful to Trump in the Hawkeye State. "Over the years, Palin has actually cultivated a number of relationships in Iowa," Robinson said. "There are the Tea Party activists who still think she's great and a breath of fresh air, but she also did a good job of courting Republican donors in the state."

Trump, meanwhile, was happy to receive the endorsement. "I am greatly honoured to receive Sarah's endorsement," he said in a statement. "She is a friend, and a high-quality person whom I have great respect for. I am proud to have her support."

NBC News noted that while Palin has increased in her attacks towards Cruz, she was an early endorser of his insurgent senate bid in 2012. Trump has also increased his attacks on Cruz, trying to put doubt on his eligibility to become president.