At least seven people were killed on Quetta's Zarghoon Road when a suicide bomber rammed into a parked police truck on Tuesday, injuring 16 people, police said.

Five policemen and two passers-by were among those killed, Inspector General of Balochistan Police Moazzam Jah Ansari told reporters. He said eight policemen were injured in the attack.

According to Associated Press, the banned Tehreek-i-Taliban Pakistan (TTP) claimed responsibility for the attack, saying a suicide bomber targeted a police contingent returning from duty at the provincial assembly building.

IG Ansari said the suicide bomber had walked up to the scene and blew himself up near the back of the police truck. He said the earlier impression that the attacker could have travelled to the truck on a motorcycle was not correct.

Bomb Disposal Squad officials said 10 kilograms of explosives had been used in the attack. Most deaths occurred due to the impact from ball bearings and pellets stored in the bomber's suicide jacket, said the IG.

IG Ansari while talking to reporters said he could "tell in advance" that the suicide bomber must have come from across the Afghan border, as DNA tests showed suicide bombers involved in previous attacks in Quetta were foreign nationals too.

He said the terrorists had targeted police in the attack and not the Balochistan Assembly, which is in the same area, as the blast occurred an hour after the assembly session had ended.

The injured, which include security personnel and civilians, were shifted to Quetta Civil Hospital's trauma centre after being administered first aid, the hospital's spokesman told DawnNews.

The explosion occurred near GPO Chowk in the vicinity of the Balochistan Assembly. The road also leads to the Chief Minister's Secretariat.

A large number of security personnel had been present near the site of the blast as a session of the Balochistan Assembly attended by almost all its members had just concluded. The area also houses several important government buildings, and is usually well secured.

A large number of security personnel and rescue services reached the site of the blast and shifted the injured to Civil Hospital Quetta, where an emergency was declared.

The area was cordoned off and media was stopped from moving near the blast site.

The incident comes less than a month after nine members of the Christian community lost their lives and 56 suffered injuries in a terrorist attack on the Bethel Memorial Methodist Church also located on Zarghoon Road. The militant Islamic State group had claimed responsibility for the attack through their Amaq news agency.

Quetta's security challenges

Balochistan has faced a number of security challenges in recent months, with security personnel in the province often being targeted in roadside explosions and suicide attacks.

Five people were killed and 27 others had suffered injuries in a suicide attack on a convoy of a paramilitary force in the Sariab Road area of Quetta in November last year.

In October, seven policemen belonging to the Rapid Response Group (RRG) of Balochistan Police and a passer-by were killed in a suicide blast, also in Sariab area.

Fifteen people, including eight soldiers, were martyred when a suicide bomber targeted a military truck near the Pishin bus stop in Quetta in August.

Earlier in June, 14 people ─ including seven policemen ─ lost their lives in a suicide blast that shook Shuhada Chowk in Quetta's Gulistan Road area.

Balochistan has been experiencing incidents of violence and targeted killings for over a decade. More than 1,400 incidents targeting the minority Shia and Hazara community have taken place in the province during the past 15 years.