"They're looking into a software problem. They're going to check everything out. When they do find a fault, they'll put it out to the rest of the world," a spokesman said, adding that other problems could be responsible for the failure.
Last Sunday, a Patriot Missile battery on the Kuwait border accidentally shot down a Royal Air Force Tornado aircraft that was returning from a mission over Iraq. Two British pilots were killed in the incident.
Then on Monday a US F-16 fighter jet fired at and destroyed a Patriot battery's radar dish after the pilot said the Patriot had "locked on" to the plane.
Published reports have linked the mishaps to software problems with the Patriot.
A Washington Post story on Tuesday quoted unnamed Pentagon officials saying that the cause of the incidents was "obviously a software glitch".
According to the newspaper, the crew of the Patriot battery had "taken cover" from incoming artillery shortly before the F-16 was locked on to by the Patriot, leaving the missile battery to operate "largely on automatic".
A story on the website of Radio Australia also quoted an unnamed British Royal Air Force commander saying that a software "glitch" led to the accidental downing of the RAF plane.
The software error caused the missile battery to read the RAF Tornado as an Iraqi missile, the report said.
Defence industry experts disagreed about the possibility of a software problem being solely responsible for downing a friendly aircraft.
"An operator has to lock on," said one expert who is familiar with the operation of the Patriot. "There's always a soldier, a man in the loop who makes the decision."
However, information on the web page of Raytheon, the manufacturer of both the Patriot and its radar system, has indicated otherwise. It lists "automated operations - including man-in-the-loop [human] override" as a "key feature" of the Patriot system.
A likely scenario has problems with the Patriot's radar combining with human error to result in friendly fire, according to Victoria Samson, a research associate at the Centre for Defense Information in Washington DC.
"A soldier at the radar might have seen something come in that didn't have a beacon and launched [a missile] before checking," Samson said.
Recent operational testing of the latest Patriot Missile, the PAC-3, revealed software problems, Samson added.