Iranian fighter jets fired multiple rounds at an unarmed US drone in international airspace over the Gulf last week, a Pentagon spokesman said.
The aircraft was on a routine surveillance flight and returned undamaged to its base.
US President Barack Obama and Defence Secretary Leon Panetta were both advised about the unprecedented incident, which occurred at about in the early hours of November 1.
Iran was later warned through diplomatic channels the US would keep conducting surveillance flights in the region and would protect its military assets, the spokesman said.
UK intelligence officials said to be providing information on targets for CIA drone strikes in Pakistan could be "encouraging or assisting murder" and the commission of war crimes, the High Court heard.
The son of a Pakistani man killed by a missile from a drone in the north-west tribal area wants a declaration that the UK Government's alleged policy of passing on information on the location of individuals to the CIA is unlawful.
Lawyers for Foreign Secretary William Hague are urging two judges to block the application brought by 27-year-old Noor Khan.
They argue that the case raises issues relating to sovereign foreign states that cannot be determined by the English courts.
They also say that adjudicating on Mr Khan's claim would plainly have a "significant impact" on the conduct of the UK's relations with the US and Pakistan in an "acutely controversial, sensitive and important" context, and also impact on relations between the US and Pakistan.
Lord Justice Moses and Mr Justice Simon are deciding over two days at the High Court in London whether the application should go to a full hearing.
A US drone attack in Pakistan killed al Qaeda's second-ranking leader, Abu Yahya al-Libi, this week but the weapon is despised by many.
The US now faces questions on whether they are becoming too reliant on drones and whether their use is causing so much resentment in Pakistan they are becoming counterproductive.
A 'US drone strike' in Yemen has killed six suspected al Qaida militants, Yemeni military officials said.
The officials, who spoke on condition of anonymity, said the attack took place near the border of Marib and Shabwa provinces south-east of the capital Sanaa.
There was no immediate word from Washington on whether it was behind the attack.