WASHINGTON (AP) — World leaders, nervously eyeing a growing threat from Islamic State militants, will seek to build a united front this week against the violent extremist group and keep it from creeping beyond its borders.

Yet international plans to counter the Islamic State group — with combined military might, diplomatic pressure on abetting partners and economic penalties — pale in comparison to the extremists’ ruthlessness and command of the swath of land it controls across parts of northern Syria and Iraq. For the second time in as many weeks, Islamic State militants released a video showing the beheading of an American journalist, and governments from Britain to Saudi Arabia to Australia warned of the potential of their citizens joining the fight — and then bringing the violence back home.