Jon Huntsman, the U.S. ambassador to China, submitted a letter of resignation Monday amid speculation that he may be pursuing a Republican presidential bid in 2012.

“We’ve received the letter. He is resigning effective April 30,” a White House aide said Monday evening.

White House Press Secretary Robert Gibbs said earlier Monday that the administration has been expecting Huntsman, who was formerly the governor of Utah, to step down in the early part of 2011.

“Ambassador Huntsman has told a number — told several people inside this building that he plans to leave … during the first part of this year,” Gibbs said during a briefing.

President Barack Obama praised Huntsman’s tenure as ambassador at a media event this month with Chinese President Hu Jintao, saying the Republican has shown his commitment to working with all parties “to advocate on behalf of our country.” Obama also joked about the possibility of being potential rivals in 2012.

“I’m sure he will be very successful in whatever endeavors he chooses in the future. And I’m sure that him having worked so well with me will be a great asset in any Republican primary,” Obama said.