Egypt vowed on Sunday to punish the attackers who killed 21 border guards in its western desert near the frontier with restive Libya

Egypt vowed on Sunday to punish the attackers who killed 21 border guards in its western desert near the frontier with restive Libya.
  
Militants firing rocket-propelled grenades and machine-guns attacked a checkpoint, 630 kilometers (390 miles) west of Cairo, on Saturday killing 21 soldiers and wounding another four.
  
The military said the soldiers were killed when an RPG set off an explosion in an ammunition depot at the El-Farafrah border security post. Egypt's presidency said "the heinous crime that took these brave souls and spilled their blood will not go unanswered".
  
"Terrorism will be uprooted from every part of Egypt. All those responsible for perpetrating these acts and acting outside of the law will receive their rightful punishment," it said.

Egypt authorities declared a three-day period of mourning from Sunday.
  
The attack followed repeated warnings by officials of a possible spillover of violence from across the border with Libya, where relentless bloodshed has sparked fears of all-out civil war.