The US is increasing the pressure on Iran by sending military planes into its airspace to test the country's defences and spot potential targets, according to an intelligence source in Washington.
The overflights have been reported in the Iranian press and the head of Iran's air force, Brigadier General Karim Qavami, declared recently that he had ordered his anti-aircraft batteries to shoot down any intruders, but there have been no reports of any Iranian missiles being launched.
"The idea is to get the Iranians to turn on their radar, to get an assessment of their air defences," an intelligence source in Washington said. He said the flights were part of the Pentagon's contingency planning for a possible attack on sites linked to Iran's suspected nuclear weapons programme.
"It make sense to get a look at their air defences, and it makes the mullahs nervous during the EU negotiations [over the suspension of Iranian uranium enrichment]," said John Pike, the head of GlobalSecurity.org, an independent military research group.
The flights come after reports of American special forces incursions into Iran. However, former US intelligence officials have said they believe the incursions are being carried out by Iranian rebels drawn from the anti-Tehran rebel group, the Mujahedin-e-Khalq, under US supervision.
The US military denied the reports. "We're not flying over frigging Iran," an official said, suggesting Tehran was making up the incidents to attract international sympathy.