THE HUFFINGTON Post has been officially recognised by the US journalism industry after winning its first Pulitzer Prize, an important milestone for the online news site.

David Wood's 10-part series on the struggles of wounded American soldiers returning home from Iraq and Afghanistan, "Beyond the Battlefield," won the Pulitzer Prize for national reporting on Monday.

Despite its robust traffic, Arianna Huffington's self-declared "internet newspaper" has fought to prove its journalistic credibility.

"It's the culmination of what we started to build almost seven years ago," Huffington said. "It's a great affirmation that great journalism can thrive on the Web."

Huffington said she believes the award changes the perception of the Huffington Post as an aggregator that draws eyeballs by recycling the journalism of other outlets.

"It definitely does," Huffington said. "Always in life, the narrative lags behind the reality."

Huffington said Mr Wood's reporting exhibited the site's commitment to original reporting and in-depth storytelling, while noting the site will remain "a platform" for distribution and aggregation.

The Pulitzer Board hailed Mr Wood's series as a "riveting exploration of the physical and emotional challenges facing American soldiers." (Jeff Donn of The Associated Press and Jessica Silver-Greenberg of The Wall Street Journal were finalists.)

The Washington-based political news site Politico also won for Matt Wuerker's political cartoons. Online news organisations were made eligible to receive Pulitzers in 2009.

"It has felt like over the last five years or so that the kind of reporting that I've always aspired to, which is deep, thoughtful, hard reporting is at risk of being swept away by new media," said Wood, a veteran correspondent of Time Magazine, the Los Angeles Times and others. "So it was with great astonishment that when I went to the Huffington Post they were very encouraging of that kind of journalism."

Mr Wood, spent about eight months on the series, also credited his editor, Timothy O'Brien, executive editor of the Huffington Post.

"The real differentiator between old media and new is how we relate to and interact with our audience," said Mr O'Brien, who previously oversaw a Pulitzer finalist for The New York Times. "We see it as setting the table for an ongoing discussion that we plan to stay on for a long time."

Roy Harris Jr, author of "Pulitzer's Gold: Behind the Prize for Public Service Journalism" and a contributor to Poynter.org, called the win "an eyebrow-raising step into respectability" for the Huff Post. He believes the Pulitzer jurors are looking to reward online-only journalism.

"Being acknowledged with a Pulitzer Prize is a groundbreaking move for any news organisation," said Mr Harris. "For the Huffington Post, being an online publication, it's got to be especially gratifying."

"Clearly it marks an arrival of a sort for the Huffington Post," said Ken Doctor, author of "Newsonomics: Twelve New Trends That Will Shape the News You Get." "It has steadily built itself from being only an aggregator to a site that has picked off a number of top journalists in the country and added them on top of the aggregation, which is a very smart business model."

Huffington, who has remained as president and editor in chief of The Huffington Post Media Group after selling the site to AOL last year for $315 million, says the site will "continue doing multi-part series on big issues." It currently has 26 reporters working a series on poverty in America.

But the Pulitzer breakthrough for the Huffington Post came, ironically or not, from old-fashioned reporting.

"The kind of reporting that I did varies not at all from the kind of reporting that I was doing 10 or 20 or even 30 years ago," said Mr Wood. "Except I'm better at it now."