Protesters try to set fire to the outside fence of the U.S. embassy in Baghdad, Iraq on Dec. 31, 2019. Photo:Xinhua

Three mortar rounds on Saturday struck Balad air base, which houses US troops in Iraq's central province of Salahudin, without causing human casualties, a provincial security source said.

The attack took place in the evening when the mortar rounds landed on Iraqi army warehouses within Balad air base, north of the Iraqi capital Baghdad, the source told Xinhua on condition of anonymity.

Balad air base is the largest military air base in Iraq, also known by the US forces as Logistics Support Activity (LSA) Anaconda.

The source also said that the US drones flew over the air base.

The attack came as a Katyusha rocket landed on the heavily fortified Green Zone in central Baghdad.

The attacks took place after a US drone attack ordered by President Donald Trump killed Qassem Soleimani, commander of the Quds Force of Iran's Islamic Revolution Guards Corps, and Abu Mahdi al-Muhandis, deputy chief of Iraq's paramilitary Hashd Shaabi forces.

The attack took place on the Baghdad International Airport's road early on Friday.

Iran's Supreme Leader Ayatollah Ali Khamenei and President Hassan Rouhani have vowed to retaliate against the US over Soleimani's death.

Over 5,000 US troops have been deployed in Iraq to support the Iraqi forces in the battles against Islamic State (IS) militants, mainly providing training and advising to the Iraqi forces.

The troops are part of the US-led international coalition that has been conducting air raids against IS targets in both Iraq and Syria.