TORONTO -- Iran’s promise of “harsh retaliation” for a U.S. airstrike that killed a top Iranian general has sent Twitter into a frenzy, with many users suggesting the Third World War is imminent.

The death of General Qassem Soleimani by American drones in Iraq has escalated an already tense relationship between the U.S. and Iran, causing his name to trend on Twitter Friday, alongside such hashtags as “#WWIII”.

“Jan 1st: New decade going fairly well, all things considered. Jan 2nd: Australia appears to be on fire. Jan 3rd: World War III announced,” read one tweet, shared more than 27,000 times.

In a statement, the Pentagon said that Soleimani "was actively developing plans to attack American diplomats and service members in Iraq and throughout the region." 

The U.S. urged citizens to leave Iraq "immediately" as fears mounted that the strike and any retaliation by Iran could ignite conflict in the region.

At the same time, American Twitter users took to their timelines to make jokes about the possibility of being drafted to the army in the event war breaks out.

Some users even drew comparisons to the killing of Archduke Franz Ferdinand, whose assassination is associated with the chain of events that led to the First World War.

“Every history nerd that has ever wondered what it would’ve been like if Twitter was around when Franz Ferdinand was killed, it’s this,” read one tweet.

Even the Scottish rock band Franz Ferdinand was forced to weigh in on the issue, thanks to its namesake, tweeting “For the record, we think #WWIII is a bad idea.”

Trump confirmed that he ordered the killing of Soleimani because he was “plotting to kill” many Americans, tweeting an image of the American flag shortly after news of his death broke.

But Trump himself has become a focus of the social media reaction, with many users unearthing old tweets with conflicting messages, including a 2011 tweet in which Trump claims former President Barack Obama would “start a war with Iran” to get re-elected.