US President Donald Trump has warned Iran the US has identified 52 targets it will hit if any Americans are harmed.
In a number of tweets on Saturday night he warned that the US will hit the targets "very fast and very hard".
He said the 52 Iranian targets represent the 52 US citizens held hostage at the US embassy in Tehran for more than a year starting in late 1979.
"Iran is talking very boldly about targeting certain USA assets as revenge for our ridding the world of their terrorist leader who had just killed an American, & badly wounded many others, not to mention all of the people he had killed over his lifetime, including recently hundreds of Iranian protesters," he tweeted.
"He was already attacking our Embassy, and preparing for additional hits in other locations. Iran has been nothing but problems for many years.
"Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD. The USA wants no more threats!"
It comes after Iran threatened to avenge the assassination of Iranian military commander Qassem Suleimani in Iraq.
Earlier on Saturday pro-Iran factions ramped up pressure on US installations across Iraq with missiles and warnings to Iraqi troops.
In the first hints of a possible retaliatory response, two mortar rounds hit an area near the US embassy in Baghdad on Saturday.
Almost simultaneously, two rockets slammed into the Al-Balad airbase where American troops are deployed, security sources said.
The Iraqi military confirmed the missile attacks in Baghdad and on al-Balad and said there were no casualties. The US military also said no coalition troops were hurt.
While no one claimed the attacks in Baghdad, a hardline pro-Iran faction in Iraq's Hashed al-Shaabi military network shortly after urged Iraqis to move away from US forces.
"We ask security forces in the country to get at least 1,000 meters away from US bases starting on Sunday at 5pm (1400 GMT)," said Kataeb Hezbollah.
The deadline would coincide with a parliament session on Sunday which the Hashed has insisted should see a vote on the ouster of US troops.
Washington has blamed the vehemently anti-American group for a series of rocket attacks in recent weeks targeting US diplomats and troops stationed across Iraq.
US Secretary of State Mike Pompeo hit back on Twitter saying Kataeb Hezbollah's "thugs are telling Iraqi security forces to abandon their duty to protect (the US embassy in Baghdad) and other locations where Americans work side by side with good Iraqi people.
"The Iranian regime telling Iraq's government what to do puts Iraqi patriots' lives at risk. The Iraqi people want out from under the Iranian yoke; indeed, they recently burned an Iranian consulate to the ground," he wrote, referencing the November sacking of the Iranian consulate in the southern city of Najaf by a protest movement angry at the government and its backers in Iran.
The US strike on Baghdad international airport early Friday killed a total of five Iranian Revolutionary Guards and five members of Iraq's Hashed.
Among the dead was Hashed's deputy head Abu Mahdi al-Muhandis, a top adviser and personal friend to Suleimani.
Trump has said Suleimani was planning an "imminent" attack on US personnel in Baghdad and should have been killed "many years ago".
Iran's supreme leader Ayatollah Ali Khamenei promised "severe revenge" for Soleimani's death and Tehran named Suleimani's deputy, Esmail Qaani, to succeed him.
Tens of thousands of Iraqis including Prime Minister Adel Abdel Mahdi, political leaders and clerics attended a mass ceremony on Saturday to honour Suleimani and the other victims.