U.S. intelligence has picked up increased chatter among Islamist terror networks approaching the 13th anniversary of the 9/11 attacks and amid the continuing battle for supremacy between Al Qaeda and the Islamic State, current and former U.S. officials told TheBlaze.

“We’ve noticed a significant increase in chatter among Islamic terrorist organizations overseas both on the Internet and phone lines,” said a U.S. government official, speaking on condition of anonymity because he was not authorized to speak on the matter. “This is certainly concerning, but as of yet we can’t pinpoint what or if they are planning a particular attack. We did see this kind of increase in chatter before the September 11 attacks. We just hope the public continues to remain vigilant.”

Intelligence agencies have registered similar spikes in threats to the U.S. ahead of previous 9/11 anniversaries. Adding to the concern, however, is Al Qaeda’s competition for dominance over the Islamic State, after the two terror groups had a falling out of sorts earlier this year. “Core” Al Qaeda is led by Ayman al-Zawahri, who is fighting to maintain leadership with Muslim followers from his base in Pakistan. The Islamic State, led by Abu Bakr al-Baghdadi, has defied orders from Zawahri and his brutal tactics have gained him prominence on a global scale with young Muslims.

This undated image shows a frame from a video released by Islamic State militants Tuesday, Aug. 19, 2014, showing the killing of journalist James Foley by the militant group. Foley, from Rochester, N.H., went missing in 2012 in northern Syria while on assignment for Agence France-Press and the Boston-based media company GlobalPost. (AP Photo)

This undated image shows a frame from a video released by Islamic State militants Tuesday, Aug. 19, 2014, showing the killing of journalist James Foley by the militant group. Foley, from Rochester, N.H., went missing in 2012 in northern Syria while on assignment for Agence France-Press and the GlobalPost. (AP)

“The threat is two-fold because ISIS is in war with core Al Qaeda,” former CIA case officer Brian Fairchild said. “ISIS was kicked out of Al Qaeda in February and they’ve been fighting each other internally for leadership. ISIS is winning right now. They have captured the imagination of young Muslims from around the world and depriving Al Qaeda of its own fighters. Al Qaeda is split down the middle and now you have 9/11 [anniversary approaching]. It would be beneficial to both camps that on 9/11, some great attack in the United States takes place. It’s certainly a serious consideration because they are both vying for primacy.”

Fairchild, who ran clandestine operations in seven CIA stations around the world and most recently served in Afghanistan in 2012, told TheBlaze that even though there is no way to say with certainty whether terror groups will strike on 9/11, there is enough intelligence to suggest the Islamic State and Al Qaeda are attempting to do so.

Fairchild said the email sent by the Islamic State to the parents of journalist James Foley a week before the video of his execution was released was actually a declaration of war on America after U.S. airstrikes on the group in Iraq.

“A message to the American government and their sheep-like citizens: We have left you alone since your disgraceful defeat in Iraq. We did not interfere in your country or attack your citizens while they were safe in their homes despite our capability to do so,” the letter said. “You do not spare our weak, elderly, women or children so we will NOT spare yours! You and your citizens will pay the price of your bombings.”

“If you look at that letter and you put it all that together you realize that this beheading was a staged and managed situation,” Fairchild said. “That communication was all part of the stage-managed deal and they justify it because they said since you killed our weak, elderly and children … Foley is now the first casualty and the second will be America. What’s concerning is if Baghdadi wants to maintain his current position as leader, he has to follow through with his threats.”

White House officials alluded Tuesday that they are seeking allied support for extended airstrikes in Syria. It is not certain if or when the strikes would take place, but the New York Times reported Wednesday that France and Great Britain may be on board.

Some reports have indicated that there may be as many as many as 300 Americans fighting alongside the Islamic State in Iraq and Syria, and thousands more from the European mainland.

“The group’s leaders have talked openly about fighting the United States and its ambitions to attack the West may be growing in conjunction with ISIL’s territorial expansion,” a U.S. intelligence official told TheBlaze.

The official said the U.S. is monitoring all possible threats in conjunction with European allies, watching for any signs that the Islamic State’s “focus is shifting externally” beyond Syria and Iraq.

Follow Sara A. Carter (@SaraCarterDC) on Twitter