A previously unknown extremist group has said it carried out Friday's bomb attack.一个从未听说过的极端分子组织声称他们组织了周五的炸弹袭击。

a marked rise in extremist violence极端暴力事件的明显上升

The country needs a strong intelligence service to counter espionage and foreign extremists.该国需要强大的情报机构来打击间谍活动和外国极端分子。