On December 31, 2019, U.S. President Donald Trump tweeted that he held Iran responsible for the December 27 attack on the K-1 airbase in Iraq's Kirkuk governorate, in which an American contractor was killed, as well as for the December 31 attack on the U.S. embassy in Baghdad by Iran-backed Shi'ite militias (in response for the December 29 U.S. attack on forces of the Popular Mobilization Forces – PMU).
Trump's tweets (source: Twitter.com/realDonaldTrump, December 31, 2019)
In response to Trump's statements, Iranian spokesmen threatened the U.S. not to act against Iran and expressed support for the actions of the Shi'ite militias.
It should be noted that, while Iranian Supreme Leader Ali Khamenei denied Iran's responsibility for the attacks on Americans in Iraq, his mouthpiece, the daily Kayhan, bragged about the attack on the embassy, calling it "the latest slap in the face" delivered by Khamenei to America.
The following are some of the Iranian reactions to Trump's threats.
Iraqi rioters at U.S. embassy in Baghad (Source: aljazeera.com, December 31, 2019)
Khamenei To The U.S.: We Will Deal An "Indisciminate Blow" To Anyone Threatening Iran
Responding to Trump's statements in a January 1, 2020 speech in Tehran, Iran's leader Khamenei said that the American attacks were revenge for the PMU's actions against ISIS (not for the attack on the Americans in the Kirkuk base), and warned the U.S. that Iran would deliver an "indescriminate blow" to anyone who threatens it. The following are excerpts from the speech posted on his Twitter page:
"Notice what [the Americans] are doing in Iraq and Syria. [They are] taking revenge on the PMU [for its actions] against ISIS. The PMU ran ISIS into the ground and exhausted [this group], which was created [by America], so now they are taking revenge. The [Iranian] government, nation and I harshly condemn this American atrocity.
"Do you see the extent of the anti-American extasy throughout Iraq? Mister [Trump] again tweeted that [the Americans] hold Iran responsible. You are mistaken! If Iran wants to fight some country, it will do so openly. We are committed to the interests and the honor of our nation, and if anyone threatens us, we will confront him and deal [him] an indiscriminate blow." 
Regime Mouthpiece Kayhan: Khamenei Has Delivered A Slap To America's Face In Baghdad
In contrast to Khamenei, who was careful not to claim responsibility for the attacks on the Americans, Kayhan took pride in the attack on the U.S. embassy in Baghdad by the Iran-backed Shi'ite militias, stating that the U.S. has once again been humiliated by Supreme Leader Khamenei. Kayhan compared this to the "humiliation of Britain" in the late 19th century by the senior Iranian cleric Mullah Ali Kani, who, according to the daily, prevented the Persian Shah, Nasir al-Din Qajar, from granting Britain extensive concessions and thereby prevented a national disgrace. It added: "The Leader [Khamenei] has slapped the masters of Britain – the Americans – in the face numerous times, the most recent of which was yesterday in Baghdad."
Iranian Foreign Ministry Spokesman Moussavi To America: Be Careful And Avoid Unwise Action
Iranian Foreign Ministry Spokesman Abbas Moussavi rejected Trump's accusations and warned the Americans of the consequences of "miscalculation" on their part, and added: "The bewildering insolence of the American officials has reached the point where, after killing at least 25 people and wounding many [other] Iraqis, they deludedly attribute their own vicious actions – the financial losses caused to [Iraq], the violations of its sovereignty and the complaints of the Iraqi people – to Iran. How, and based on what logic, do you [Americans] expect the Iraqi people to remain silent in the face of this crime? The Americans disregard the Iraqi people's demand for freedom and independence, while at the same time they forget their role in supporting Saddam [Hussein] and creating ISIS, and later in murdering and robbing the Iraqi people. They also seem to forget that the Iraqi people still regard them as an occupier." Moussavi called on the White House to reconsider its "destructive" policy in the region.[iv]
Foreign Ministry Spokesman Abbas Moussavi (source: Mehr, Iran, January 1, 2020)
Iran's UN Ambassador Takht-Ravanchi: America's Accusations Against Iran Are Intended To Draw Attention Away From Its Killing Of Iraqis
Iranian Ambassador to the UN Majid Takht-Ravanchi said that Washington was accusing Iran in order to cover up its "brutal killing" of Iraqis: "America’s accusations against Iran are intended to divert attention from the recent brutal killing and also from 17 years of occupation in Iraq which have cost the lives of over 300,000 innocent Iraqis... The PMU and its branches are a purely Iraqi [force], acting under the control of Iraq’s democratic and legitimate government. They have played an important role in fighting and defeating the ISIS terrorists, and today they are the most important guarantee against the resurgence of this terrorist group."
Iranian Journalist: "The Americans Will Not Be Secure In Iraq"
Iranian journalist Hossein Dalirian, previously a senior editor at the Tasnim news agency, affiliated with Iran's Islamic Revolutionary Guards Corps (IRGC), tweeted that the Americans will no longer be secure in Iraq, mentioning that the resistance has heat-seeking missiles for use against Apache helicopters: "Unlike those who have written that the Apache helicopters of the American army are dropping flyers to intimidate the protesters at the U.S. embassy, I believe that these helicopters are dropping flyers due to the fear of the heat-seeking missiles of the resistance. Starting today, it seems that the Americans will not be secure in Iraq."
Hanizade, An Expert Close To The IRGC: "The Anti-American Riots Will Intensify From Day To Day"
On January 1, 2020, political analyst Hassan Hanizade, who is close to the IRGC, said: "Since the latest American attack on the PMU base in Al-Anbar, which caused the deaths of 25 of the fighters of this popular militia, the situation in Iraq has changed completely. This attack reveals a new conspiracy orchestrated by America, the Zionist regime and Saudi Arabia against the sovereignty and independence of Iraq. The American attack on the PMU positions has changed the picture, and the Iraqi people have realized that America is attempting to destroy the security of their country and to orchestrate a civil war in Iraq. That is why they spontaneously gathered outside the U.S. embassy. This led to a confrontation with the protesters and even prompted U.S. helicopters to take to the air, intensifying the rage and the invective directed at the U.S.
"Now the conditions have become very difficult for America, and an extensive presence of U.S. forces in the country is no longer possible. The Americans did not think that an attack on the PMU fighters would increase the Iraqis' unity. Now they falsely accuse Iran [of being responsible].
"America attacked on Iraqi soil... and this is an attack on international law and a violation of it. According to the Iraqi government, the PMU is a force operating within the Iraqi armed forces and follows their laws. Therefore, an attack on the fighters of this force is tantamount to an attack on the military and armed forces of this country, and all the Iraqi political streams, even the opposition, responded harshly to this attack and condemned it.
"The riots against America in Iraq will intensify from day to day. The goal of the Americans is to affect the relationship between Iran and Iraq, and to that end [they] accuse Iran of mobilizing its agents against the U.S. embassy. But [in reality] it is Washington which, by perpetrating the military attack [on the PMU], created a serious challenge to its continued presence in Iraq."