ISLAMABAD, Pakistan (CNN) -- Gunmen fired on a children's aid group in Pakistan's tribal region Monday, leaving three staffers dead and at least one critically injured, the organization said.
And earlier Monday a suicide bomber struck Pakistan's military headquarters in Rawalpindi Monday, killing at least eight people, including the army's top ranking medical officer and himself, military officials said.
Lt. Gen. Mushtaq Ahmed Baig, the army surgeon-general, was among those killed in the blast in Rawalpindi, the officials said.
The non-governmental organization, Plan, said that at around 4:15 p.m. up to a dozen men carrying guns and grenades entered the office in Mansehra, in the North West Frontier Province -- Pakistan's lawless tribal region bordering Afghanistan. The gunmen began firing and detonated three explosive devices.
Video from the scene showed the building engulfed in smoke and flames as staffers tried to escape from windows. Others were carried out by hand or on stretchers. The fire destroyed the building.
Plan's chief executive, Tom Miller, said the office immediately shut down as security teams looked into the incident.
"Our primary concern is for our staff and the families of those hurt in the attack," Miller said in a written statement. The motive for the attack remains under investigation. Officials were not aware of any prior threats to the office, Plan spokesman Jon Slater told CNN.
Slater said 21 full-time and seven part-time employees work at the office, though it's unclear how many were present at the time of the attack. Most of the employees are locals.
Plan, which helps Pakistani communities provide education and other opportunities to children, has had a presence in the region for more than a decade. The group says it was deeply involved in the relief effort following a major earthquake in 2005 that left nearly 3 million people homeless.
At least 20 others were wounded in the Rawalpindi suicide bombing which happened along Mall Road, a heavily traveled thoroughfare in Rawalpindi, according to Pakistani officials. Watch the aftermath of the suicide bombing »
The government promoted Baig to lieutenant general last January and he assumed his role as army surgeon-general the following month, according to a news release at the time.
Baig, who graduated from a Lahore medical college, was an ophthalmologist.
Rawalpindi, which lies just outside Islamabad, is a closely guarded city and home to Pakistan's military headquarters. It has, in recent months, experienced several suicide bomb attacks -- including the recent assassination of Benazir Bhutto.
The government blames the attacks on militants operating out of the country's northwest tribal areas that border Afghanistan.
In early February, a suicide bomber rammed his motorcycle into a van carrying army medics, killing at least four people.
Opposition leader and Pakistan's former Prime Minister Benazir Bhutto was killed at a rally in the city on December 27. A bomber blew himself up near her limousine, and videotape showed a gunman firing toward her vehicle as she left the rally.
Both the Pakistani government and British investigators concluded that she died from the suicide blast, not from a gunshot wound. Violent riots in the wake of her death forced the postponement of parliamentary elections.
The government contends that Bhutto's killing was orchestrated by Baitullah Mehsud, the leader of the Pakistani Taliban who has ties to al Qaeda. The CIA reached the same conclusion.
Two months before Bhutto's assassination, a suicide bomber detonated an explosive near the army headquarters -- which houses President Pervez Musharraf's office -- killing six people and wounding 10 others.
Musharraf who was inside his office at the time of the blast was not injured. Musharraf survived two assassination attempts in the city in 2003.
And in September, two suicide bombers blew themselves up, killing at least 25 people. One attack targeted a bus carrying government employees. The other involved a suicide bomber who crashed his motorcycle into cars.