Buildings shook and windows broke as another rocket, the fourth fired by US warplanes into the Iranian territory since Friday, landed outside the southern Iranian city of Khorramshahr on Saturday, IRNA reported.

Residents in the city heard a strong explosion at 15:55 (1125 GMT). IRNA reporters in Khorramshahr are trying to locate the site of the blast.

Meanwhile, two severe blasts rocked the city of Abadan at 16:35 Friday. The explosions were succeeded by a column of smoke and dust across from the border inside the Iraqi territory.

Residents in the cities along the Arvand-Rud river have put tapes on the windows of their houses to prevent them from breaking as intermittent explosions on the other side of the river in Al-Faw Peninsula and other Iraqi cities have become a rule.

Abadan was hit by the first rocket, fired by US warplanes, into the Iranian soil on Friday, in which three people were injured.

Two more American rockets landed at a village in southwest Iran Saturday, but there was no immediate word on probable casualties or property damage.

The two rockets hit the village of Manyuhi in Arvand-Kenar near the border with Al-Faw Peninsula, a military commander said in Shalamcheh.

Abadan governor, Jamal Alemi, said that US warplanes had violated the Iranian airspace above the city five times Friday night. There were reports of further violations on Saturday.

"American airplanes violated the Iranian airspace five times between 18:30 (1500 GMT) and 19:00 until the dispatch of this report," he told IRNA Friday night.

"Around 19:00 today (Friday), an American plane was sighted at a high altitude, which fired a rocket into one of the (oil) depots," he added.

"Three citizens, including a guard of the depot, were injured and taken to hospital. They left hospital after receiving treatment," Alemi said.

The rocket caused a strong boom and panic among citizens who rushed out of their homes in panic, a police official in Abadan said.

Iran, which fought an imposed war between 1980 and 1988 with Iraq -- then a close American ally -- has reiterated that it will not back one side or another in the US-led war.

The Islamic Republic, however, has strongly condemned the invasion.