Iran yesterday spurned a "brazen" request by the US president for the return of a captured CIA surveillance drone, saying Washington should instead apologise for invading its airspace.
"The American espionage drone is now Iran's property," said the country's defence minister, Ahmad Vahidi.
An Iranian parliamentarian, Hamid Resaei, described the spy plane as "war booty".
US officials are concerned that Iran, with help from Russia or China, may be able to unlock the chemical composition of the drone's radar-deflecting coating or replicate its engine, control systems, cameras and sophisticated sensors.
The Islamic republic has captured a prize that "can blunt the US technological edge over its adversaries", Iran's semi-official Fars news agency boasted on Monday.
A senior Iranian parliamentarian said the country has the ability to reverse engineer the drone and mass-produce a superior version.
The US suffered another embarrassing drone loss yesterday when one crashed at an airport in the Seychelles.
Washington uses the archipelago as a base for drones targeting Al Qaeda-linked militants in Somalia.
Analysts said that if Iran can tap the drone's secrets, it could discover what facilities the US was spying on and help Tehran take countermeasures with its air defence systems.
The US had reportedly mulled over plans to go into Iran to recover or destroy the drone but decided not to in case it led to a clash with the Islamic republic.
That decision was attacked yesterday by the former vice president of the US, Dick Cheney, who called the drone's downing a "significant intelligence loss".
He added that its retrieval "would have been a fairly simple operation".
Barack Obama's administration had "basically limited itself to saying 'please give it back'", he said.
Iranian media said Mr Obama's plea for the drone's return put the US in the role of a "beggar".
The unmanned aircraft was reportedly on a mission to spy on Iran's nuclear facilities when it crashed under mysterious circumstances 240 kilometres inside Iranian territory on December 4, delivering Tehran a propaganda windfall.
Iran's president, Mahmoud Ahmadinejad, said on Monday: "The Americans have perhaps decided to give us this spy plane."
The episode has raised tensions between Washington, which insisted the drone malfunctioned, and Tehran, which said it was brought down through a cyber-attack on its avionics by Iran's Revolutionary Guards.
On Monday Mr Obama gave the first official US confirmation that the drone, a boomerang-shaped RQ-170 Sentinel, was in Iran's hands when he made a formal request for its return.
"We have asked for it back," he said. "We'll see how the Iranians respond."
US officials, including the secretary of state, Hillary Clinton, doubted Iran would comply. They were promptly proved right.
Mr Vahidi insisted yesterday that the "American espionage drone is now Iran's property". "Instead of apologising to the Iranian nation, it [the US] is brazenly asking for the drone back," he added.
Iran's foreign ministry was similarly scornful.
"It seems that he [Mr Obama] has forgotten Iran's airspace was violated, spying operations were undertaken, international laws were violated and that Iran's internal affairs were interfered with," said Ramin Mehmanparast, the ministry's spokesman.
The head of Iran's parliamentary national security committee, Parviz Sorouri, said on Monday that Iran was in the "final stages" of decoding the drone's software and would use the information gleaned to sue the US for the "invasion" of its airspace.
Iranian experts, he added, would go on to "reverse engineer" the drone and mass-produce a better version.
Views vary among US officials about the seriousness of any security breach resulting from the loss of a drone to Iran.
The US defence secretary, Leon Panetta, said much depended on the condition of the aircraft, which was paraded virtually intact on Iranian television last Thursday.
The US air force chief of staff, General Norton A Schwartz, said last week that there was "a potential for reverse engineering".
But other US experts doubt that Iran has the technology to clone the drone without help from China or Russia, and said any data on board was likely to be encrypted and of little value to an adversary.
Iran's semi-official Mehr news agency has reported that Russian and Chinese officials are clamouring to inspect the captured drone to copy its cutting-edge stealth technology.
Both countries are building their own stealth aircraft, including drones.
But Mr Sorouri insisted Tehran could and would do it alone. "This great defensive capability is reserved for us, and we are not ready to share it with others," he said.
The episode has deepened Iranian suspicions that the US and Israel are waging an intensifying campaign of covert operations aimed at derailing Iran's suspected quest for nuclear weapons - an ambition Tehran denies.
Iran yesterday said it had indicted 15 people on charges of spying for the US and Israel but did not elaborate on the nationality of the suspects, nor say when they were detained.
Iran periodically announces the capture of or execution of alleged US or Israeli spies, but rarely provides any further information.