ISLAMABAD, Pakistan (CNN) -- A suicide attacker killed 16 people Sunday, 12 of them police officers, near a protest rally marking last year's Pakistani government raid on the Red Mosque, police said.
Emergency vehicles arrive after a Sunday blast in Pakistan kills several people.
The rest of those killed were civilians, Islamabad police said. Fifty-three people were injured.
Video showed the bodies of police officers lying on the side of the road, while other seriously injured police officers and civilians were loaded onto stretchers and taken to waiting ambulances.
The attacker struck the police position on a roundabout around 8 p.m., near the rally and a marketplace. 
Watch the chaotic aftermath »
The police were stationed at the outermost security perimeter, part of a protection cordon set up by the government for Sunday's rally, according to Islamabad police Inspector General Asghar Gardezi.
It's unclear if the suicide attacker was on foot or in a vehicle.
Pakistan's acting Interior Minister Rehman Malik said about 12,000 people attended Sunday's rally, which marked the first anniversary of government forces storming Islamabad's Red Mosque, or Lal Masjid.
Malik, who went to the blast site shortly after the attack, said there were no lapses in security at Sunday's rally.
Last year's July 10 raid -- ordered by President Pervez Musharraf, who was Pakistan's army chief at the time -- ended a weeklong bloody standoff between military forces and Islamic extremists.
More than 100 people died when the security forces stormed the mosque. Most were radical students holed up inside, but the deaths included some women and children as well.
The raid was intended to rout Islamic extremists who hoped to establish a Taliban-style rule across the capital.
Instead, it increased suicide attacks on civilians, police and security forces. It also led to the collapse of a controversial cease-fire between Musharraf's government and tribal leaders in the lawless territories along Pakistan's border with Afghanistan.
The 2006 truce was blamed for establishing a safe haven for Taliban and al Qaeda leaders in Pakistan's tribal regions.
Musharraf's popularity further plummeted following the raid. His grip on power was already tested by widespread protests earlier in 2007, prompted by his dismissal and house arrest of Chief Justice Iftikhar Chaudhry.
A month after the Red Mosque raid, Musharraf considered imposing a state of emergency in Pakistan, senior government officials said, citing the growing security threat in the tribal regions.
The officials said Secretary of State Condoleezza Rice helped talk him out of imposing the measure, which his critics claimed was merely a ploy to regain power and silence his political opponents.
He eventually imposed a six-week state of emergency in early November, suspending the constitution and sacking dozens of judges.
That move ended up rallying more Pakistanis behind Musharraf's political opponents and helped the opposition win control of the government in February elections.
Although he remains president, Musharraf's power has eroded since the elections and since he abandoned his position as army chief last year.
Despite the controversial 2006 truce under Musharraf's government, the civilian leaders are negotiating with tribal leaders in the lawless border region, but military operations in the tribal areas against Taliban militants are still ongoing.
Last weekend, the military launched an operation near Peshawar -- the capital of the North-West Frontier Province -- its biggest push against extremists in the tribal region since the civilian government took power in March.
CNN's Zein Basravi contributed to this report.
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