Former Utah governor and Republican presidential candidate Jon Huntsman Jr. has accepted President Trump's offer to be the U.S. Ambassador to Russia, Fox News has confirmed.

Sources told Fox that Trump called Huntsman Monday to offer him the job. If confirmed, Huntsman would head to Moscow at a time when relations between the U.S. and Russia have reached a low point in the post-Cold War era amid investigations of possible contacts between Trump's campaign and Russian officials.

Hunstman's acceptance also ends speculation about a possible primary challenge against Utah Sen. Orrin Hatch, who is up for re-election next year.

Huntsman previously served as U.S. Ambassador to China between 2009 and 2011, when he resigned to launch a bid for the 2012 Republican nomination. He dropped out of the race after finishing third in the New Hampshire primary and endorsed eventual nominee Mitt Romney.

Huntsman was elected governor of Utah in 2004 and re-elected in 2008. He resigned seven months into his second term to become ambassador to Beijing.

Huntsman had an up-and-down relationship with Trump during last year's campaign. He was slow to endorse any candidate for the Republican nomination though did back Trump once he became the presumptive nominee. But Huntsman then called for Trump to drop out after the October release of a 2005 video in which Trump is captured on a hot microphone making lewd comments about women.

He said then that the "campaign cycle has been nothing but a race to the bottom" and called for Trump's running mate, then-Indiana Gov. Mike Pence, to top the GOP ticket.

Trump also went after Huntsman during his tenure as ambassador to Beijing. In a series of tweets in 2011 and 2012, the celebrity businessman called Huntsman a "lightweight" and "weak" and claimed that China "did a major number on us" during his tenure.

Huntsman's daughter, Abby, is a co-host of "Fox & Friends Weekend."

Fox News' John Roberts and the Associated Press contributed to this report.