President Donald Trump warned Saturday that the US is targeting 52 sites in Iran and will hit them "very fast and very hard" if the Islamic republic attacks American personnel or assets. In a saber-rattling tweet that defended Fridays US drone strike killing of a powerful Iranian general in Iraq, Trump said 52 represents the number of Americans held hostage at the US embassy in Tehran for more than a year starting in late 1979. Trump said some of these sites are "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!" Late Saturday night, the president tweeted again, this time warning Iran that the US will hit Iran "harder than they have ever been hit before!" Trump followed up with another tweet, saying the US would use its "brand new beautiful" military equipment "without hesitation" if the Iranians retaliate. Trump spoke out after pro-Iran factions ramped up pressure on US installations across Iraq with missiles and warnings to Iraqi troops -- part of an outburst of fury over the killing of Qasem Soleimani, described as the second most-powerful man in Iran. With the Islamic republic promising revenge, his killing was the most dramatic escalation yet in spiraling tensions between Washington and Tehran and has prompted fears of a major conflagration in the Middle East. In the first hints of a possible retaliatory response, two mortar rounds hit an area near the US embassy in Baghdad on Saturday, security sources told AFP. Almost simultaneously, two rockets slammed into the Al-Balad airbase where American troops are deployed north of Baghdad, 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. With Americans wondering fearfully if, how and where Iran will hit back for the assassination, the US Department of Homeland Security issued a bulletin that said "at this time there is no specific, credible threat against the homeland." However on Saturday the website of the Federal Depository Library Program, a little-known US government agency, was breached by a group claiming to be linked to Iran, who posted graphics displaying the Iranian flag and vowing revenge for Soleimanis death. - Direct war - While no one claimed Saturdays attacks in Baghdad, a hardline pro-Iran faction in Iraqs Popular Mobilization Forces shortly after urged Iraqis to move away from US forces by Sunday at 5:00 pm local time (1400 GMT). The deadline would coincide with a parliament session which the PMF 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. Many fear the US strike that killed Irans military mastermind Soleimani would set off a wider conflict with Iran, and have braced for more attacks. The US strike on Baghdad international airport early Friday killed a total of five Iranian Revolutionary Guards and five members of Iraqs PMF. Among the dead was Abu Mahdi al-Muhandis, the de facto leader of Iraqs PMF umbrella body of paramilitary groups. He was also a top adviser and personal friend to Soleimani. As head of the Guards foreign operations arm, the Quds Force, Soleimani was a powerful figure domestically and oversaw Irans wide-ranging interventions in regional power struggles. Trump has said Soleimani was planning an "imminent" attack on US personnel in Baghdad and should have been killed "many years ago".