Iranian leaders are calling for "vengeance" after a U.S. airstrike in Baghdad killed a top general.
In the days since the attack, U.S. officials warned of an anti-American hack on a government website, President Donald Trump threatened to hit dozens of Iranian targets if the country retaliates, and authorities around the U.S. have beefed up security as a precaution.
Here's everything Americans should know about this attack and its implications:
What happened, exactly?
Around midnight Friday, an armed American drone struck a top Iranian military general, who was in his vehicle on an access road near the Baghdad airport in Iraq. He was the target of the attack.
Who was the Iranian general killed?
Gen. Qassem Soleimani was the head of Iran's elite Quds Force.
The 62-year-old is credited as the architect of Iran's regional military alliances, responsible for forging close ties to militant groups and political factions throughout the Middle East.
Soleimani rose to prominence by advising forces fighting the Islamic State group in Iraq and in Syria to support President Bashar Assad.
Iran's Supreme Leader Ayatollah Ali Khamenei called him the "international face of resistance." Soleimani remains popular among many Iranians, who see him as a selfless hero fighting Iran's enemies abroad.
The strike also killed Abu Mahdi al-Muhandis, deputy commander of Iran-backed militias in Iraq known as the Popular Mobilization Forces, and five others, including the PMF's airport protocol officer, Mohammed Reda, Iraqi officials said.
Why was Soleimani killed?
The Defense Department said it killed Soleimani because he "was actively developing plans to attack American diplomats and service members in Iraq and throughout the region."
It also accused Soleimani of approving the two-day attacks on the U.S. Embassy in Baghdad earlier this week.
Tensions between Iran and the United States have continued to grow since Trump withdrew from nuclear deal and imposed crippling sanctions in 2018.
Will the United States go to war with Iran?
While the attack certainly raised fears of outright war, it is too early to determine how -- or if -- tensions will escalate.
Iran has vowed "harsh retaliation" for the U.S. airstrike, and President Donald Trump tweeted Saturday that America is prepared to hit 52 targets in the Islamic Republic "very fast and very hard," including some important to "the Iranian Culture," if it retaliates.
Targeting cultural sites could be considered a war crime under international agreements to which the U.S. belongs, according to both Trump's political foes and former national security officials. Secretary of State Mike Pompeo assured the U.S. would only hit "lawful targets."
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....— Donald J. Trump (@realDonaldTrump) January 4, 2020
The United States will deploy 3,500 troops from Fort Bragg's 82nd Airborne Division to the Middle East in anticipation of a possible attack overseas.
Iran has allies throughout the region -- in Iraq, Syria, Lebanon, Yemen and the Gaza Strip -- who received aid, arms and training from Tehran.
A retaliatory attack overseas could include anything from challenging U.S. warships in the Persian Gulf, firing ballistic missiles or deploying allies. The United States has relatively small deployments of troops in the area who could be targeted in revenge attacks.
There's also a chance Soleimani's killing, and the possibility of war, may discourage Iran from responding swiftly or at all.
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Should Americans be concerned?
While there are currently no specific or credible threats against the homeland, U.S. federal officials are cautioning Americans to remain vigilant in public, at home and abroad.
The Department of Homeland Security warned of an apparent hack of a federal website: The Federal Depository Library Program displayed an image of a bleeding Trump with an Islamic Revolutionary guard's fist in his face Sunday.
The DHS is also telling the public to be wary of cyber disruptions. Americans are urged to watch out for suspicious emails and network delays and encouraged to implement multi-factor authentication on devices.
Law enforcement in big cities like New York and Los Angeles are ramping up security measures, as areas with high population densities are more vulnerable to attack.
Have spoken with Commissioner Shea + Dep Commissioner Miller about immediate steps NYPD will take to protect key NYC locations from any attempt by Iran or its terrorist allies to retaliate against America. We will have to be vigilant against this threat for a long time to come.— Mayor Bill de Blasio (@NYCMayor) January 3, 2020
The United States urged its U.S. citizens to leave Iraq "immediately" on Thursday.
Iraq's Parliament called for the expulsion of U.S. forces from the country Sunday. A pullout of the estimated 5,200 American troops could cripple the battle against ISIS and allow its resurgence.
Global powers warned Friday that the world has become a more dangerous place and urged restraint.
The Secure Community Network, the nation's top organization dedicated to protecting synagogues and Jewish institutions, also urged Jewish communities to be vigilant and report suspicious activity.
"The potential for threats to the Jewish communities outside of Israel cannot be disregarded," a statement issued Thursday read. "Hezbollah and Iran have in the past responded to attacks via overseas terrorism, such as the 1994 suicide truck bombing of the AMIA Jewish community center in Buenos Aires, Argentina, and the 1992 attack at the Israeli Embassy in Buenos Aires."
What else happens now?
Oil prices surged and most major global stock markets declined Friday after news of the killing.
Benchmark U.S. crude climbed $2.19 to $63.37 per barrel in electronic trading on the New York Mercantile Exchange.
What does this mean for President Trump?
Trump was vacationing on his estate in Palm Beach, Florida, at the time of the airstrike but sent out a tweet of an American flag.
The dramatic attack comes at the start of a year in which Trump faces both a Senate trial following his impeachment by the Congress and a re-election campaign. It marks a potential turning point in the Middle East and represents a drastic change for American policy toward Iran after months of tensions.
Several Trump opponents have criticized the president for the attacks, and more recently, for tweeting a threat to target "important to Iran & Iranian culture" if the country retaliates to the killing of its top general.
Democratic presidential candidate Joe Biden called this tweet "incredibly dangerous and irresponsible."
House Speaker Nancy Pelosi suggested that "Congress and the American people are being left in the dark about our national security."
But Trump allies were quick to praise the attacks. "To the Iranian government: if you want more, you will get more," tweeted South Carolina Sen. Lindsey Graham.
The Associated Press and ABC News contributed to this report.