BAGHDAD — Four Katyusha rockets hit an Iraqi military base that houses U.S. contractors Monday without causing any casualties, Iraq’s military said in a statement.

The rockets hit Balad air base in northern Iraq at 8 p.m. local time, the statement said. Security forces launched a large-scale security operation to search for whoever launched the strike.

The incident was the latest in a string of attacks in recent weeks in Iraq that have targeted mostly installations that house Americans.

There was no immediate claim of responsibility for Monday’s attack, but U.S. officials have previously blamed Iran-backed Iraqi militia factions for such assaults.

The last time the base was struck was April 18, when multiple rockets exploded wounding two Iraqi security forces. Days later, multiple rockets targeted a military base near Baghdad airport, which houses U.S. troops.

Calls for U.S. troop withdrawals from Iraqi lawmakers grew after a U.S.-directed drone strike killed Iranian Gen. Qassem Soleimani and an Iraqi militia leader in Baghdad in January 2020. A non-binding resolution passed by parliament urged the government to oust all foreign troops from Iraq.

These developments spurred strategic talks between Baghdad and Washington that focused primarily on the future of the U.S. troop presence in the country. In late 2020, the U.S. troop level in Iraq was reduced to 2,500 based on orders from the Trump administration.