Pakistan's Taliban has claimed responsibility for an attack by two suicide bombers against recruits leaving a paramilitary training center in Pakistan on Friday.
At least 80 people were killed in the blasts. The group said the attack was in retaliation for the death of Osama bin Laden.
Emergency medical teams raced to treat more than 150 people injured in the morning explosion at a military training center in northwestern Pakistan.
There are reports that 800 recruits were boarding vans to leave a graduation celebration when two suicide bombers drove up on motorcycles and set off their bombs.
"I heard the blast, ran towards the spot to find out what happened, and suddenly the second blast took place," one resident recalled.
"There may be a desire on some al Qaeda members to exact revenge and that's something that we have to be vigilant about," President Barack Obama said in response. "And we're monitoring all these situations."
The Somali wing of al Qaeda includes 27-year-old Omar Hammami, an American born and raised in Alabama who threatened the president this week.
"Today we remind Obama and the rest of his cronies that they have entered the wrong war," he said.
The Pakistani Taliban called Friday's attack revenge for the death of bin Laden.
Meanwhile, pro-Islamist lawyers protested America outside Pakistan's high court, and attended special prayers for Osama bin Laden.
Secretary of Defense Robert Gates promised extra protection for the families of the Navy SEAL team that killed the al Qaeda leader. Bin Laden's followers have threatened the men and their loved ones.
The identities of SEALs and other special forces are kept secret but details of the Pakistan operation filtered out through the media.