A Katyusha rocket crashed Sunday into Baghdad's Green Zone, landing less than a mile from the sprawling U.S. Embassy, an Iraqi military spokesman said.

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

It was the first such attack since September, when three mortar shells landed in an abandoned lot inside the Green Zone.

There was no immediate comment from the State Department or the U.S. Embassy in Iraq on Sunday's attack.

Associated Press reporters on the east side of the Tigris River, opposite the Green Zone, heard an explosion, after which alert sirens sounded briefly in Baghdad.

Iraqi military spokesman Brig. Gen. Yahya Rasoul told The Associated Press that a Katyusha rocket fell near the statue of the Unknown Soldier, less than a mile from the U.S. Embassy. He said the military is investigating the cause but that the rocket was believed to have been fired from east Baghdad. The area is home to Iran-backed Shiite militias.

Iraq's state-run news agency said a Katyusha rocket crashed inside the Green Zone without causing any casualties.

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

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

The American embassy in Baghdad -- the world's largest -- lies within the fortified neighborhood, also known as the International Zone, which is surrounded by concrete walls.

The apparent attack comes amid heightened tensions across the Persian Gulf, after the White House ordered warships and bombers to the region earlier this month to counter an alleged, unexplained threat from Iran. The U.S. embassy in Baghdad and its consulate in the northern city of Irbil also evacuated non-essential staff this week.

Iran and the United States have both said they do not want war as tensions between them increase.

American forces withdrew from Iraq in 2011 but returned in 2014 at the invitation of Iraq to help battle the Daesh terror group after it seized vast areas in the north and west of the country, including Iraq's second-largest city, Mosul. A U.S.-led coalition provided crucial air support as Iraqi forces regrouped and drove Daesh out in a costly three-year campaign. Iranian-backed militias fought alongside U.S.-backed Iraqi troops against Daesh, gaining outsized influence and power.

Now, amid an escalating conflict between the U.S. and Iran, Iraq is once again vulnerable to becoming caught up in the power play. An attack targeting U.S. interests in Iraq would be detrimental to the country's recent efforts at recovering and reclaiming its status in the Arab world.

On May 8, Pompeo made a previously unannounced trip to the Iraqi capital following the abrupt cancellation of a visit to Germany, and told Iraqi intelligence that the United States had been picking up intelligence that Iran is threatening American interests in the Middle East, although he offered no details according to two Iraqi officials.

A few days later, as U.S.-Iranian tensions continued to rise, the State Department ordered all non-essential, non-emergency government staff to leave the country.

Employees of energy giant ExxonMobil have also begun evacuating from an oil field in the southern Iraqi province of Basra.