Iran claimed to have downed an American drone Tuesday – and displayed a Boeing-built ScanEagle as proof – but the Pentagon issued a denial with some wiggle room, as the risks of a military confrontation continued to escalate over Tehran's murky nuclear program.

Iran's propaganda coup, the second time in a year it has displayed a downed drone, also pulled back the curtain on the steady increase in spying and probing of defences by all parties, as the United States and Israel prepare for the possibility of war to deny Tehran's ruling mullahs from getting nuclear weapons.

Both President Barack Obama and Israeli Prime Minister Benjamin Netanyahu have vowed to keep Iran out of the select nuclear-weapons-capable club of nations.

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Spying drones, cyber-warfare and the assassination of Iranian scientists are all part of the – mostly deniable – escalation. On Tuesday, the White House dodged questions about the missing drone.

"We have no evidence that the Iranian claims you cite are true," said White House spokesman Jay Carney. Iran, however, broadcast a video showing two Revolutionary Guards officers examining the evidently intact and apparently undamaged ScanEagle, an unarmed drone that is in use in the military of the U.S., Canada and several other Western nations.

"All our active unmanned aerial vehicles working here have been accounted for," said a spokesman for U.S. Navy's Fifth Fleet, based in Bahrain, which commands dozens of U.S. warships, including a battle groups led by a nuclear-powered aircraft carrier patrolling the Persian Gulf.

Whether or not the grey, swept-wing ScanEagle proudly displayed on Iranian TV and described as being "captured" belonged to the U.S. military, an American intelligence agency or – perhaps – a previously undisclosed buyer of the system such as Israel or Saudi Arabia, there seemed little doubt that it was real.

A year ago, a far more powerful and sophisticated U.S. spy drone, the stealthy, high-tech RQ-170 Sentinel, was captured when Tehran apparently hijacked its guidance system. That loss was initially met with vague denials by U.S. officials, followed by suggestions that the drone displayed by Tehran was a fake.

Both sides are using drones, although only rarely do the secret surveillance flights become known – such as when one gets shot down or is captured. In October, an Iranian-made drone was shot down by an Israeli F-16 warplane over the Negev Desert. It had apparently launched from Hezbollah-controlled areas of Southern Lebanon.

The ScanEagle apparently downed by Iran was also a relatively short-range drone, unlike, for instance the high-altitude, jet-powered Global Hawk that can fly from bases in the U.S. to Afghanistan and back and stay aloft for 36 hours.

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ScanEagles were originally developed for searching for tuna at sea by Insitu Inc., a company later bought by Boeing Corp. They can be launched from and recovered by small vessels such as fishing boats.

Last month, the Pentagon accused Iran of attempting to shoot down an American Predator – a larger, sometimes armed, drone that has been used for assassination strikes against al-Qaeda and Taliban targets.

/Iran's Foreign Minister Ali Akbar Salehi said the ScanEagle capture was the latest evidence of American violations of Iranian sovereignty. "We will use this drone as evidence to pursue a legal case against American invasion in international forums," he said.

The increasing use of unmanned aircraft both to spy on and attack adversaries underscores their political advantages and cost effectiveness. Although the United States retains a significant lead in the number and types of drones, other countries, including Israel and Iran, have devoted massive efforts to develop indigenous drone technologies.

"Obviously when you have an unmanned aircraft, there is no risk of a pilot being shot down and killed or captured in hostile territory, so these unmanned aircraft make it possible to conduct operations in places where you wouldn't want to put a human pilot at risk," said John Villasenor, a professor of electrical engineering at UCLA and nonresident senior fellow at the Brookings Institution whose area of expertise includes drone operations and remote surveillance.

"They're less expensive than manned aircraft; they don't put human pilots at risk, so it's not surprising that we are seeing more [evidence of drone operations]."