WASHINGTON: An outspoken surrogate for Mitt Romney's White House campaign suggested late Thursday that race was a factor in former secretary of state Colin Powell's endorsement of President Barack Obama.

Former New Hampshire governor John Sununu told CNN that the re-endorsement of Obama by Powell -- a Republican who served in both Bush presidencies but backed Obama in 2008 -- was possibly due to both men being African-Americans.

"Frankly, when you take a look at Colin Powell you have to wonder whether that's an endorsement based on issues or whether he's got a slightly different reason for preferring President Obama," Sununu told CNN host Piers Morgan.

"When you have somebody of your own race that you're proud of being president of the United States, I applaud Colin for standing with him."

The remarks by Sununu, a prominent and often flamboyant supporter of Romney, sparked outrage on Twitter and could inject race into a campaign the Republican challenger has tried to keep focused on the sluggish US economy.

Sununu backtracked from the remarks in a media statement issued overnight, saying: "Colin Powell is a friend, and I respect the endorsement decision he made, and I do not doubt that it was based on anything but his support of the president's policies."

The remarks came just two days after Republican Senate candidate Richard Mourdock, explaining his anti-abortion stance, sparked controversy by saying that pregnancies caused by rape are "something God intended to happen."

Those remarks threatened to slow Romney's progress in winning over vital women voters in key swing states and gave Obama an opening to brand Republicans as extremists when it comes to women's rights.

Sununu's remarks could prove less damaging -- Obama already enjoys overwhelming support among African-American voters -- but may further distract from Republicans' central argument against the president's economic policies.

The two presidential candidates are locked in a virtual tie less than two weeks ahead of the November 6 election, with Romney enjoying a slight lead in national polls but Obama holding a narrow edge in vital battleground states.

Powell, who served as chairman of the Joint Chiefs of Staff under President George H. W. Bush and secretary of state under President George W. Bush, is a moderate Republican once seen as a promising presidential prospect.

In his endorsement of Obama on Thursday, Powell credited the president with recent improvements in the economy and praised him as a steely commander-in-chief who had wound down the wars in Iraq and Afghanistan.