Noble said that while he knew of no Haqqani ties to the attacks, the killings are a means of dividing the Afghans from their allies that is "right up their alley."
Jeffrey Dressler, an analyst at the Washington-based Institute for the Study of War, who has extensively studied the Haqqani network, said Friday that U.S. suspicions may be well-founded.
"If we accept the notion that a proportion of the 'insider attacks' are due to infiltration, then it is absolutely plausible to assume that the Haqqanis are responsible for a portion of those," Dressler said in an email exchange. "The tactic of 'insider attacks' is certainly a potent one, so I would also suspect that the insurgency is doing all it can to increase the frequency and lethality of the incidents."
The Haqqani network has the backing of elements within the Pakistani security establishment and is regarded as one of Afghanistan's most experienced and sophisticated insurgent organizations.
The network maintains a safe haven in North Waziristan, Pakistan, across Afghanistan's southeastern border. The Pakistani Army has consistently refused to launch a military operation in North Waziristan despite the presence there of al-Qaida senior leaders.
Australian Maj. Gen. Stephen Day, the plans chief for the international coalition's joint command, said in an interview that the Haqqanis are a more troublesome military challenge than the Taliban.
"They represent the most dangerous threat because they are the best trained, best resourced opponent we have." Day said Thursday. He was not speaking about the question of a Haqqani link to insider attacks.
When the number and lethality of insider attacks began to accelerate early this year, U.S. and coalition officials were reluctant to release details, including those cases in which the shooter missed or wounded but did not kill his target. The attacks were dismissed as isolated incidents. That changed over the summer as top U.S., Afghan and NATO officials began speaking about them more and publicly pressing for solutions.
On Friday the AP was given a previously unreleased set of data about 2012 and 2011 insider attacks.
The data show that in addition to the 53 U.S. and allied personnel killed so far this year, more than 80 have been wounded. Although the coalition had previously said there were 21 attacks killing 35 allied personnel in 2011, it had not said that another 61 were wounded.
The statistics also show a previously unreported pattern of attacks happening either in multiple locations on the same day or on consecutive days. This has been the case 10 times so far this year, and Noble said he and other officials are unable to explain the significance of this.
Associated Press writer Deb Riechmann contributed to this report.
Robert Burns can be followed on Twitter at http://www.twitter.com/robertburnsAP
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.