A Katyusha rocket was fired Sunday (May 19th) into Baghdad's Green Zone -- home to government offices and embassies, including the US mission -- days after the US evacuated staff from Iraq, citing threats from Iran, AFP reported.

"A Katyusha rocket crashed into the Green Zone without causing casualties," the Iraqi security services said in a brief statement, without giving further details.

Tensions between the US and Iran have soared in the past few weeks.

Last Wednesday the US ordered the evacuation of non-essential personnel from its embassy in Baghdad and the Erbil consulate in northern Iraq, citing "imminent" threats from Iranian-backed Iraqi armed groups.

It was not immediately clear who was behind Sunday's attack.

A police source told AFP that "initial reports indicate that the rocket was fired from an open field" in southern Baghdad.

The Green Zone is one of the world's most high-security institutional quarters.

Located in the centre of Baghdad, it houses parliament, the prime minister's office, the presidency, other key institutions, top officials' homes and embassies.

The US embassy in Baghdad lies within the fortified neighbourhood, also known as the International Zone, which is surrounded by concrete walls.