ISIS threatened Rome. At least some Italians responded with Twitter jokes.

In its videotaped killing of Coptic Christians earlier this month, the Islamic State in Libya showed a masked fighter pointing across the Mediterranean towards Europe. "We will conquer Rome, God willing," he said.

That threat was echoed in social media accounts of the extremist group and its sympathizers, and flagged by a group that monitors terrorist activity online. Rita Katz, who heads SITE Intelligence Group, posted on Twitter that ISIS militants and their allies were tweeting threats to invade Rome under the hashtag #We_Are_Coming_O_Rome. (No word on why it's "O" instead of "To").

The chaos in Libya has allowed ISIS to gain a foothold in the country, raising international alarm and real concern in Italy's government that violence in the former Italian colony could spill over the Mediterranean. Europe is also on a heightened security alert following terrorist attacks like the January shootings in Paris.

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But online, Twitter users inside and outside Italy weren't impressed with the threats of an actual invasion of Rome. Many responded with humor, and satirical warnings to ISIS fighters about the city's notorious transportation woes.

Tomorrow is strike of public transport. Good luck. #We_Are_Coming_O_Rome — Alessandro Cocco (@AleCocco84) February 19, 2015

#We_Are_Coming_O_Rome if you manage make sure to come between 1 and 5 AM otherwise no way you getting trough! pic.twitter.com/KktacE0LvP — smarteyes (@cecike) February 20, 2015

Some expressed concern that the city doesn't need more trouble:

Please stay at home. We need to solve so many issues in this city, don't add you to this long list... #We_Are_Coming_O_Rome — Graziella Giancaspro (@gragia86) February 19, 2015

#We_Are_Coming_O_Rome You're too late , Italy is already been destroyed by their governments.... — Franco (@campafranco) February 20, 2015

And some praised the Italians for their glib responses to militants' threats:

The answers to #We_Are_Coming_O_Rome are simply glorious. Bravo, Italian people. — Miguel Espés (@MiguelEL) February 20, 2015

Tnx for making my day...reading the #We_Are_Coming_O_Rome tag and loving it :D — Milica Jovic (@_Milica_Jovic) February 20, 2015

Jokes aside, Italy eyes the threat from Libya with real concern, pressing this week for swifter action by the United Nations to find a political solution to the country's ongoing conflict.

Italian islands are only a few miles from Libya, and officials are worried the deteriorating security situation will only swell the waves of migrants who have been smuggled from the North African country to Italy's shores. They also fear Islamic State-affiliated terrorists may hide among the migrants to reach Italy.