(CNN) -- The insurgents who attacked an Afghan military base where Prince Harry is deployed may have gotten onto the base by sneaking through a hole in a fence, a British military source said Monday. Officials discovered the hole after the attack, the source said, adding that the attackers -- daringly disguised in U.S. Army uniforms -- also tried to blow up parked NATO aircraft with hand-held improvised explosive devices.
Prince Harry was about a mile and a half away from Camp Bastion when the attack happened, according to the source. The royal was immediately placed on lockdown, as were other troops who were not fighting the insurgents, the source said.
U.S. Marines, British forces and a U.S. Army unit that just happened to be nearby spent nearly three hours battling the insurgents, the source said.
"This was a well-coordinated and complex attack that we're taking very seriously," a U.S. official said Monday.
It's extremely rare for Afghan insurgents to use U.S. uniforms in their attacks. The last time CNN can identify was more than two years ago, when NATO repelled attacks on two bases in Khost province in August 2010.
No coalition troops were killed in that attack, NATO's International Security Assistance Force said at the time.
At least two U.S. Marines were killed in the brazen strike late Friday, and six jets were destroyed, the ISAF said.
Well-trained, well-rehearsed fighters carried out the sustained assault in Helmand province, the ISAF said.
About 15 insurgents organized into three teams penetrated the base's perimeter fence and did considerable damage, destroying six refueling stations and damaging six aircraft hangars.
The attackers toted automatic rifles, rocket-propelled grenade launchers and suicide vests.
They destroyed six AV-8B Harrier jets and damaged two others before the attack ended, the coalition said.
Fourteen of the fighters were killed, and one was wounded and captured, the ISAF said.
Eight coalition military personnel and one civilian contractor were also wounded.
It is too soon to say whether the attackers had "inside knowledge," ISAF spokesman James Graybeal said.
The ISAF would not say how the attackers got the uniforms, but CNN staff who have spent time in Afghanistan say they are for sale in markets there.
There has been at least one other case of Afghan insurgents wearing U.S. uniforms, in May 2010.
And in Iraq five years ago, there was a dramatic and successful raid using the tactic.
Attackers wearing what appeared to be American uniforms were responsible for the kidnapping and killing of five U.S. soldiers in Karbala, Iraq, in 2007.
Prince Harry is an Apache helicopter pilot based at Camp Bastion, but the British Ministry of Defence categorically rejected reports in Sunday's British press that he was just a few hundred yards from the gunbattle.
Harry, a grandson of Queen Elizabeth II and third in line to the British throne, "was in no way in any danger" during the latest attack, ISAF spokesman Maj. Martin Crighton said earlier.
On Saturday, the ISAF said the camp is secure and the strike would not "impact" air and ground operations.
Camp Leatherneck, the U.S. side of the base, was not affected by the attack, said Maj. Adam N. Wojack, an ISAF spokesman.
The joint base is in a remote desert region of Helmand, the southern province in the Taliban heartland.
The Taliban said it carried out the strike, calling it a response to the anti-Islam film stoking anger among Muslims. Yet Crighton said there had no organized demonstrations outside its gates before the assault.
Afghanistan has seen only relatively small and peaceful demonstrations against the film during a week in which there were protests across predominantly Muslim countries and other locations.