WASHINGTON - A vocal group of conspiracy theorists known as birthers are riling the White House with their persistent claim that Barack Obama is not an American citizen and therefore ineligible to be president.

The claim that the United States' first African-American president was born in Kenya, not Hawaii, first emerged during his presidential campaign, but it has garnered more media attention in the summer silly season, a traditionally slow news period when many Americans are on vacation.

White House spokesman Robert Gibbs looked exasperated at his briefing on Monday when a reporter asked him, Is there anything you can say that will make the birthers go away?

If I had some DNA, it wouldn't assuage those that don't believe he was born here, Gibbs replied. But I have news for them and for all of us: The president was born in Honolulu, Hawaii, the 50th state of the greatest country on the face of the earth. He's a citizen.

A year-and-a-half ago I asked that the birth certificate be put on the Internet because Lord knows, you got a birth certificate and you put it on the Internet, what else could be the story?

The digitally scanned copy of the certification of live birth from Hawaii's Department of Health shows Obama was born in Honolulu at 7:24 p.m. on August 4, 1961.

The nonpartisan FactCheck.org, a project of the Annenberg Public Policy Center of the University of Pennsylvania, examined, handled and photographed the original certificate in an effort to put the controversy to rest.

We conclude that it meets all of the requirements from the State Department for proving U.S. citizenship. Our conclusion: Obama was born in the USA, just as he has always said.

FactCheck.org also pointed out that Obama's American mother and Kenyan father placed an advertisement in a local Honolulu newspaper on August 13, 1961, announcing their son's birth.

Gibbs, who has ridiculed birthers in the past, impatiently dismissed the claims as made-up, fictional nonsense. There are 10,000 more important issues for people in this country to discuss, rather than whether or not the president is a citizen.

Despite the seemingly incontrovertible evidence, the issue shows no sign of disappearing off the radar of right-wing radio talkshow hosts and others who say the birth certificate is a forgery to hide the fact that Obama is foreign-born.

Republican Congressman Mike Castle was booed at a town hall meeting after he insisted Obama, a Democrat, was an American citizen. Video of the meeting went viral and has been viewed nearly 700,000 times on YouTube.

Fellow Republican Congressman John Campbell is a co-sponsor of legislation that would in the future force presidential candidates to produce their birth certificates.

Meanwhile, several lawsuits challenging Obama's eligibility to serve as president have been dismissed; and a U.S. army major made headlines by arguing he should not be deployed to Afghanistan on the grounds that the commander-in-chief of the U.S. armed forces was not an American citizen.