Five US warplanes entered Iran's air space last Thursday night from the southwestern Shalamcheh border and flew over the city of Khorramshahr for a while, press reports said Tuesday.
According the Persian daily Seday-e Edalat, 'the jet fighters which flew at high speed and altitude, then headed to the Arvand River'.
"They flew at a height of 10 kilometers and maneuvered over Khorramshahr for a while," the paper said.
"While the objective behind the fighters' violation of the Iranian air space is not known yet, some military specialists believe such moves are aimed at assessing the sensitivity of the Islamic Republic's anti-aircraft defense system," it added.
It said military and air force officials had refrained from commenting on the incident when contacted.
Iran has been wary of the occupation forces' presence on its doorsteps in Iraq and carefully watched their movements.
Tehran, while opposing Iraq's invasion, took a position of `active neutrality' at the time of the attack.
In June, Iranian naval guards seized three British boats with eight crew in the country's territorial waters in Arvand river, which borders Iraq.
The servicemen, two Royal Navy sailors and six Royal Marine commandos, were later released.
Their equipment reportedly consisted of personal weapons, radios and navigation equipment, including echo sounders to measure the depth of the water, global positioning systems to identify the exact position and up-to-date maritime charts.