At least 13 people were killed and 85 injured when a suicide bomber struck Monday evening around 6pm outside the Punjab Assembly in Lahore during a protest, police officials said.

Inspector General of Police (IG) Punjab Mushtaq Ahmad Sukhera confirmed that six police officials were among the dead, including two senior officers.

85 people were also injured in the attack, which he said had targetted police officials present at the site.

The Jamat-ul-Ahrar claimed responsibility for the attack.

"The suicide attacker was on foot," Counter Terrorism Department (CTD) Chief Dr Mohammad Iqbal had revealed earlier.

SSP Operations Zahid Gondal of Punjab Police and DIG Traffic Lahore Capt (retd) Ahmad Mobin were among those killed in the attack.

Hours earlier, DIG Mobin had been seen on television, mediating with the protesters gathered at the site.

Mobin was reportedly at the site to negotiate with protesters for an end to the sit-in and to clear the area.

A large group of chemists and pharmaceutical manufacturers were gathered in front of the provincial assembly to protest a government crackdown against the sale of illegal drugs. There was a significant presence of law enforcers in the area while the protest was ongoing.

Up to 400 people had attended the protest, according to an AFP reporter who was on the scene when the explosion occurred.

Rescue services, including ambulances and fire tenders, reached the scene soon after the attack. An emergency was also declared in all hospitals of Lahore. Majority of the casualties were shifted to Mayo Hospital and Ganga Ram Hospital.

Contingents of Pakistan Army and Rangers also reached the site.

The security forces cordoned off the area with tents, with the inner cordon taken over by Army personnel. Forensic teams were collecting evidence and had started initial investigations.

Prime Minister Nawaz Sharif condemned the attack and reiterated Pakistan is in decisive fight against terrorism while praising the sacrifices of the slain security personnel.

Chief of Army Staff General Qamar Javed Bajwa instructed local military commanders and intelligence agencies to provide all necessary assistance to civilian authorities and arrest those responsible, a statement issued by the Inter-Services Public Relations (ISPR) read.

Terror alert

In a Feb 7 notification addressing the Home Secretary, Punjab, the Provincial Police Officer and DG Pak Rangers Punjab, the National Counterterrorism Authority (NACTA) had warned of a possible terrorist attack in Lahore.

NACTA had directed that all vital installations, including important buildings, hospitals and schools, be kept under strict vigilance.

"Extreme vigilance and heightened security measures are suggested to avoid any untoward incident," the notification added.

Punjab Law Minister Rana Sanaullah said that maximum preparations were made after the threat alert was received.

“The spot where the blast took place is always under threat. Even if there was no alert, strict security measures are always taken in the area.”