The leaders of some European countries hardest hit by recent militant attacks use this week's UN general assembly to corner representatives from the likes of Facebook and Google over efforts to combat extremism online.

Facebook, Twitter, Microsoft, and Google are all in attendance at the gathering in New York.

It's not clear exactly what the leaders will do if the corporations don't comply.

But the European Union has already threatened legislation if they don't step up.

Twitter has said it purged almost 300,000 extremist accounts in the first half this year, although it's a 20 percent decline from prior six months.