The Green Zone houses government buildings and foreign embassies.
The spokesman said that "attacks on USA personnel and facilities will not be tolerated and will be responded to in a decisive manner" and added that the US will hold "Iran responsible if any such attacks are conducted by its proxy militia forces or elements of such forces". The Trump administration has provided no evidence for the claim, which has been received with skepticism and mistrust from some American lawmakers and European and Iraqi allies, who suspect the United States of politicizing the diplomatic spat with Iran.
Qais al-Khazali, the leader the Iranian-backed Asaib Ahl al-Haq, or League of the Righteous group, tweeted that he is opposed to operations that "give pretexts for war" and added that they would only "harm Iraq's political, economic and security conditions".
Tensions in the Gulf have escalated significantly over the past two weeks after the USA accelerated the dispatch of an aircraft carrier and moved B-52 bombers to the region.
That same month the USA shut its consulate in Basra and ordered all but emergency staff to leave the southern port city hit by weeks of protests and relocate to Baghdad.
When asked by a reporter on Thursday whether or not the USA was going to war with Iran, President Trump replied, "I hope not".
The US embassy is seen in the heavily fortified green zone in central Baghdad, Iraq.
Police were now searching for suspects and the rocket launcher in the eastern district of New Baghdad, he said. The area is home to Iran-backed Shiite militias.
The Iraqi spokesman's remarks come after the Sky News Arabia broadcaster reported on Sunday that several rockets fell in the Green Zone, not far from the US Embassy. These attacks were believed to have been carried out by Yemen's Houthi fighters in retaliation for the prolonged Saudi war against Yemen.
President Donald Trump has tightened economic sanctions against Iran, and his administration says it has built up the US military presence in the region.
USA soldiers would be "easy to defeat", said Commander Hossein Salami in a statement.
A year ago Trump pulled the United States out of a 2015 pact that limited Iran's nuclear program in return for the lifting of worldwide sanctions.
State Department officials acknowledged in a separate statement that no entity had yet taken responsibility for the attacks, but that Washington would hold Tehran accountable should its Iraqi proxies be deemed responsible for the strike.
Iran FM holds talks with Sushma Swaraj amid tensions with US
Iran is its third largest supplier after Iraq and Saudi Arabia and meets about 10 per cent of its total needs. Zarif, who is on a two-day visit to India, had said the United States is escalating tensions "unnecessarily".
"These militias, some of which are aligned with Iran, are answering to Iraq, but there may be rogue elements?" asked Saberi.
The UAE on Sunday said that the current "critical circumstances" in the region required a "unified Arab and Gulf stance".
According to United States media reports, Trump's long-hawkish national security advisor John Bolton is pushing a hard line on Iran, but others in the administration are resisting.
The other two vessels in the attack were registered in the UAE and Norway.
The meetings will be a "significant opportunity for the countries of the region to achieve their aspirations for establishing peace and stability", it said. "The ball is in Iran's court and it is up to Iran to determine what its fate will be".
Also on Sunday, the Saudi Media Ministry said Crown Prince Mohammed bin Salman had discussed regional developments and the need to strengthen security in a call to US Secretary of State Mike Pompeo.
Trump has been at odds with the U.S. European allies but supported by the Saudis and Israelis ever since he pulled out past year of an worldwide agreement on Iran's nuclear energy.
The commander of Iran's powerful Islamic Revolutionary Guards Corps, General Hossein Salami, said his country is not looking for war, but is not afraid of a confrontation, either.
On May 15, the U.S.
The Mehr news agency quoted Iranian army chief warning the United States against miscalculations.
Hormuz is a very narrow strait between the Persian Gulf and the Gulf of Oman, through which the majority of oil tankers heading for the West must pass.