Tehran, April 4 : Iran has rejected a US proposal for a 48-hour ceasefire, the semi-official Fars news agency reported on Friday.

The proposal was delivered to Iran through a "friendly" country on Thursday, Fars quoted an informed source as saying.

Washington has stepped up its diplomatic efforts to secure a ceasefire, particularly after an Iranian strike targeted a US "military forces depot" on Kuwait's Bubiyan Island, Xinhua news agency reported quoting sources.

According to Fars, assessments suggest that the proposal was put forward following an intensification of the crisis in the region and "serious problems" for US forces resulting from their country's "miscalculation" of Iran's military capabilities.

The report added that Iran's response to the offer was not given in writing, but through the continuation of attacks in the battlefield.

Meanwhile, the Iranian army confirmed that its air defence systems shot down a US A-10 "Warthog" attack plane over Iran's southern waters near the Strait of Hormuz, with the aircraft crashing into the Persian Gulf.

The announcement came shortly after IRGC said that it had downed a US F-35 fighter jet in central Iranian airspace earlier in the day. Later Friday, Iran's semi-official Mehr News Agency reported that a US Black Hawk helicopter was also hit by a projectile in Iranian airspace while searching for the pilot of the downed US fighter jet.

Yadollah Rahmani, governor of Kohgiluyeh and Boyer-Ahmad province, called on residents in tribal and rural areas to assist authorities in locating "enemy pilots."

On February 28, Israel and the United States launched joint attacks on Tehran and several other Iranian cities, killing Iran's then Supreme Leader Ali Khamenei, along with senior military commanders and civilians. Iran responded by launching waves of missile and drone strikes targeting Israel and US assets in the Middle East.

/IANS