This story has been clarified. Read below

The NFL has found that 11 of the New England Patriots' 12 game balls were inflated significantly below the NFL's requirements, league sources involved and familiar with the investigation of Sunday's AFC Championship Game told ESPN.

The investigation found the footballs were inflated below what's required by NFL regulations during the Pats' 45-7 victory over the Indianapolis Colts, according to sources.

"We are not commenting at this time," said Greg Aiello, the NFL's senior vice president of communications.

League sources have confirmed that the footballs were properly inspected and approved by referee Walt Anderson 2 hours and 15 minutes before kickoff, before they were returned to each team.

ESPN Sports Radio 810 in Kansas City reported that the Patriots' footballs were tested at the half, reinflated at that time when they were found to be low, then put back in play for the second half, and then tested again after the game. The report did not reveal the results of the test following the game. All of the balls the Colts used met standards, according to the report.

Meanwhile, a source told WEEI.com that the Patriots used 12 backup balls for the second half against the Colts after issues were found with most of the originals. Patriots spokesman Stacey James confirmed that the team had 24 balls total available, WEEI reported.

Under NFL rules, no alteration of the footballs is allowed once they are approved. If a person is found breaking league rules and tampering with the footballs, that person could face up to a $25,000 fine and potentially more discipline.

Troy Vincent, the league's senior executive vice president of football operations, told The Associated Press late Tuesday in response to this report that the "investigation is currently underway, and we're still awaiting findings." He told "Pro Football Talk with Mike Florio on NBC Sports Radio" earlier Tuesday that the NFL expected to wrap up its investigation in "two or three days."

Sources earlier this season told ESPN NFL Insider Adam Schefter that the Colts had concerns about underinflated balls after their regular-season game against the visiting Patriots on Nov. 16.

During that game, Colts safety Mike Adams twice intercepted Tom Brady and gave the balls to the Colts' equipment manager to save -- and both times there were concerns about the balls feeling underinflated, sources told Schefter.