Former U.S. House of Representatives speaker Newt Gingrich used social media to announce Wednesday he is running for the Republican Party's presidential nomination to challenge Barack Obama.

In a post on Twitter, Gingrich said, "Today I am announcing my candidacy for president of the United States."

In a YouTube video, Gingrich told viewers, "There's a much better American future ahead."

Gingrich, 67, who first indicated on Monday through his Twitter and Facebook accounts that he was set to make the announcement, had told followers he has been "humbled" by the encouragement he has received.

Gingrich has long laid hints of a run and has been raising money for months.

The former Georgia congressman gained national recognition in his years opposing the Clinton administration in the 1990s after leading the Republicans to their first majority in the House in 40 years.

Gingrich left Congress in 1999, but has stayed in the public eye in recent years through writing and on-air commentary with Fox News.

He joins an already-crowded field of Republicans expected to vie for the party's nomination for the 2012 presidential race, including former Massachusetts governor Mitt Romney, former Alaska governor and vice-presidential candidate Sarah Palin, as well as billionaire businessman and reality show star Donald Trump.

John Huntsman, the former U.S. ambassador to China, is also exploring a run, as are former Minnesota governor Tim Pawlenty and Mitch Daniels, the current governor of Indiana.

Meanwhile, Obama, the Democratic incumbent, is enjoying his highest approval rating in two years — 60 per cent —following his order of a Navy SEAL raid last week that killed al-Qaeda leader Osama bin Laden.

According to an Associated Press-GfK poll conducted after the raid, more than half of Americans now say Obama deserves to be re-elected, despite a sluggish recovery from the global recession and the country's unemployment hovering around nine per cent.

With files from The Associated Press