BAGHDAD (Reuters) - A barrage of about a dozen rockets struck near Baghdad’s fortified Green Zone diplomatic and government compound on Sunday evening in what appeared to be one of the biggest strikes in weeks.

The rockets could be heard whistling past from the east of the Iraqi capital as they flew in the direction of the riverside compound and exploded, Reuters correspondents on the opposite river bank said.

The strikes took place during a heavy sandstorm. U.S. forces normally use helicopters to retaliate against fighters who target the Green Zone, but sandstorms prevent the helicopters from flying, letting fighters strike with impunity.

U.S. and Iraqi forces say Shi’ite militiamen have fired more than 700 rockets and mortars over the past month, many aimed at the Green Zone and most fired from the capital’s Sadr City slum, stronghold of the Mehdi Army militia of Shi’ite cleric Moqtada al-Sadr.

U.S. forces have occupied the part of Sadr City closest to the centre in an effort to reduce the rocket attacks, but have not moved further into the slum.