Republican White House hopeful Newt Gingrich has angrily denounced President Obama's apology to Afghan President Hamid Karzai over the burning of Korans at a U.S. military base.

The former speaker took to his Twitter feed to condemn Obama's letter to Karzai, saying: "It is an outrage that on the day an Afghan soldier murders two American troops, Pres. Obama is the one apologizing."

The incident at Bagram Air Base triggered a violent response from Afghans, with 14 dead over three days of protests. Two American soldiers were shot dead when an Afghan soldier turned his weapon on them at their base in Khogyani in eastern Nangarhar province, district governor Mohammad Hassan told AFP.

Obama's apology mirrored that given by then-President George W. Bush in April after an American sniper in Afghanistan shot a Koran, peppering the Muslim holy book with bullet holes. At the time, White House spokeswoman Dana Perino had emphasized that it was important to show that the US president "knew that this was wrong."

Ahead of Gingrich's vitriolic comment, Obama spokesman Jay Carney told reporters aboard Air Force One that the apology was "wholly appropriate, given the sensitivities to this issue, the understandable sensitivities."

"His [Obama's] primary concern as Commander-in-Chief is the safety of American men and women in Afghanistan, of our military and civilian personnel there," said Carney. "And it was absolutely the right thing to do."

Asked whether Obama was concerned that Republicans might seize on the letter to reinforce their charges that Obama too-easily apologizes for the United States, Carney replied: "That's a fully false, fallacious and ridiculous narrative that is not borne out by any facts."

More popular Yahoo! News stories:

• Obama defends his energy policy in Florida speeach, after coming under fire for high gas prices

• How the iphone is changing the way Washington thinks: Machine Politics

• 'Parks and Recreation' funnyman Aziz Ansari talks about hosting an Obama fundraiser and doing standup for the President

Want more of our best political stories? Visit The Ticket or connect with us on Facebook, follow us on Twitter, or add us on Tumblr. Handy with a camera? Join our Election 2012 Flickr group to submit your photos of the campaign in action.