After years of apparent lull, al-Qaida members were seen gathered in large numbers in what is now interpreted as an assembly with potentially dangerous intent.

The al-Qaida members seen in the video are escapees from Yemen prison who are greeted by al-Qaida's number two-in-command, Nasir al-Wuhayshi, at an undisclosed place in Yemen, according to NBC News.

Various jihadist websites had broadcast the video, which finally brought it under the scanner of the US officials who now say that the clip is authentic.

Experts are examining the clip which also shows al-Wuhayshi saying that he wanted to attack and eliminate the US.

The video of the al-Qaida gathering was captured by a non-profit terrorism-tracking watchdog, the Terrorism Research and Analysis Consortium (TRAC), and put on YouTube.

"This is quite an extraordinary video," Paul Cruickshank, terrorism analyst, told the CNN.

In the speech, Al Qaida in Arabian Peninsula (AQAP) leader al-Wuhayshi is heard saying, "We must eliminate the cross. ... The bearer of the cross is America!"

Officials believe that such a gathering possibly suggests rehearsal for another attempt at a terrorist attack, which could be in the planning stages.

"The U.S. intelligence community should be surprised that such a large group of al Qaida assembled together, including the leadership, and somehow they didn't notice," said CNN national security analyst Peter Bergen.

"His message to the United States was very much the same as (former al-Qaida leader Osama) bin Laden's: 'We're coming after you,' " said Cruickshank.

A top Sharia official for AQAP and a former Guantanamo Bay detainee, Ibrahim al-Rubeish, is also seen in the clip.

Republican Mike Rogers, chairman of the House Intelligence Committee told the CNN newscast 'The Situation Room with Wolf Blitzer' that he was not sure if CIA had prior information on the meeting, but he thought that such group sessions were more frequent than generally assumed.

He was then asked by Blitzer if the US would have sent drones to kill the high-profile militants, to which Roger replied that "there are a lot of procedures that one would go through ... to do an airstrike on any large package of individuals."

"It's difficult to get assets in position. You have to know where they are and where they meet at the right time in the right place with the right equipment. That's a lot to do."

Retired General Mark Kimmitt told 'CNN Tonight' that the terror groups could pose a direct threat to the US, and it was important to plan ahead.

"The question isn't why didn't we know," he said. "The question is: What are we going to do about it?"

However, other US officials say no conclusions can actually be drawn from the video as the clip in itself was uneventful, but unusual.

"The depiction of such a large gathering of fighters and the appearance of senior leaders are atypical of AQAP's propaganda videos," a US intelligence official told NBC News.