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Democratic presidential candidate Sen. Barack Obama (D-IL) speaks to supporters during a campaign rally at the Fort Worth Convention Center in Fort Worth, Texas February 28, 2008. More than 11,000 people attended the event, his third of the day. Obama and Sen. Hillary Clinton (D-NY) are locked in a tight race headed into the Texas primary election on March 4, 2008. (UPI Photo/Ian Halperin)

The Hill reported that endorsement came as Obama, the junior senator from Illinois, is being criticized by rival Sen. Hillary Clinton on his foreign policy credentials.

Rockefeller said Obama's opposition to the Iraq war in 2002 is among the reasons he chose to endorse him, the newspaper reported.

"The indisputable fact is Barack Obama was right about Iraq when many of us were wrong," Rockefeller said in a statement. "It was a tough call and the single greatest national security question, and mistake, of our time."

Rockefeller's endorsement came the same day Clinton released a campaign ad in Texas, ahead of the Lone Star State's Tuesday primary, suggesting it would be preferable to have Clinton in the White House in case of a national security crisis.

Obama called the ad a scare tactic, The New York Times (NYSE:NYT) reported.

"We've seen these ads before," Obama said. "They're the kind that play on people's fears to try to scare up votes."