מטוס F-16 אמריקאי טס מעל סוריה

And one public intelligence analyst is suggesting that the incursion was no accident, but a deliberate attempt to check for Iraqi forces preparing for war.

Air Force and Pentagon officials said the plane, part of the Operation Northern Watch mission patrolling the no-fly zone over northern Iraq, accidentally flew over Syria for about 23 minutes without incident before crossing into Iraq, just south of the 36th parallel.

Syrian officials have not filed a formal protest, said Greg Sullivan, a State Department spokesman in Washington, D.C. Sullivan said that U.S. officials approached their Syrian counterparts immediately after the incursion, explaining that the jet had a technical malfunction. He said that Syrian forces neither shot at the single-engine fighter nor even engaged it with radar.

Officials at the Syrian embassy in Washington, D.C., did not return repeated calls.

American officials also informed Turkish officials of the incident, said Frank Woods, a spokesman at the American Embassy in Ankara. "There were probably military-to-military conversations," but Turks - who grant the United States and Britain permission to fly ONW missions from their base - filed no formal protests, Woods said. A source at Turkey's Office of External Affairs said last Friday that he was unaware of the over-flight, adding that Syria had not lodged any protests with Turkey.

Sullivan characterized the incident as a relatively brief incursion: "It was 15 minutes in, 15 minutes out." Sullivan added that it's not uncommon for American planes to inadvertently cross into other countries' territory. Still, the incursion comes only five months after Chinese fighter pilots forced a Navy EP-3 surveillance plane to land, then held its crew for 11 days.

And one retired Air Force aviator calls it "bizarre" that a single American plane could leave an ONW sortie, which typically includes at least 40 planes. "A pilot under AWACS control just flies into Syria for a half-hour without his wingman? That's not the way we do things," said the source, who asked to remain anonymous.

Rear Adm. Craig Quigley was quoted last week as saying that an AWACS command-and-control plane monitored the pilot, but could not get him back on course.

"We had an AWACS aircraft up and saw that he was steering wrong, that he was into Syrian airspace, and called him out, and he got out of Syrian airspace," Quigley said. Asked why the crew of the AWACS allowed the pilot to fly off course for 23 minutes, Quigley declined to discuss ONW operational details.

Stratfor.com, an Austin, Texas-based commercial intelligence company, offered its own explanation in an Aug. 17 report - the F-16 was on a reconnaissance mission, looking for signs of Iraqi troop build-ups in Syria in preparation for an all-out war with Israel. Last month, Iraqi papers announced that Saddam Hussein was preparing a jihad, or holy war, to "liberate" Palestine, where Israeli and Palestinian authorities have been fighting since early this year.

"The more likely explanation is that the multi-role fighter was sent on a reconnaissance mission over Syria," stated the unsigned report. The F-16 is not usually the first choice for reconnaissance; satellites and reconnaissance aircraft can carry out such missions, stated the report.

But if Washington was trying to spot ground forces, "the F-16 could have acted as a decoy, attempting to goad camouflaged troops into revealing their presence and identities through electronic emissions such as air-defense radars and communications."

An analyst at Sentinel - a division of Jane's Sentinel Information Group - has a more prosaic explanation.

The F-16 went off course, and the Syrians simply missed it, said Jeremy Binnie, Sentinel's Middle East analyst. "Twenty-three minutes is a very long time for a modern jet to fly off-course, and it does seem very strange" that Syrian fighters didn't intercept, Bennie said.

But he said that Syria has most of its sophisticated military equipment in the southwest, close to bitter enemy Israel, and the disputed border with Lebanon. The more stable border with Turkey could be protected by relatively obsolete S-300 Soviet-made radar, he said.

Moreover, Syria only has two airbases in the north - al-Qamishli in the northeast on the Turkish border and Dayr az Zawr in east-central area near Iraq.

From those bases, Syria could have scrambled sophisticated Russian-built MiG-29s, he said. "But they probably couldn't get locked on [the F-16], to be honest," he said. And that, said Bennie, is not something that the Syrians are going to rush to acknowledge.