The death toll of Friday morning's suicide blast in Pakistan's northwest tribal area has shot to 50 while some 70 others were injured, of whom about 20 are said to be in critical condition, according to local media reports.

Early Friday morning, an unidentified miscreant who tried to force into a political agent's office located at a crowded bazaar in the town of Tehsil Yakaghand in Pakistan's northwest tribal area of Mohmand Agency detonated the bomb carried with him, causing a huge casualty on the spot.

According to the local media reports, the blast took place outside the office of an assistant political agent which is said to house an estimated 50 people inside at the time when the blast went off. Several shops and vehicles near the office were seriously damaged and the electricity and telephone systems near the blast site also collapsed.

Police have cordoned off the area after the blast and rescue work is right underway. More rescue personnel are being dispatched from the nearby city of Peshawar, capital of Khyber Pakhtunkhwa province in northwest Pakistan.

Police sources said following the blast 27 suspected criminals held under police custody in an adjacent venue escaped during the chaos.

About 20 critically injured people in the blast have been shifted to the Road Reading Hospital of Peshawar, a Xinhua reporter in Peshawar confirmed.

Media teams are barred from entering the blast site.

The motive behind the suicide blast is not known yet. It is also not known whether the suicide bomber was killed or not in the blast.

So far no one has claimed the responsibility for the blast.

This is the third most serious suicide bomb attack which happened in the country within the past ten days. Late on last Thursday night, three suicide bombers attacked a shrine in Pakistan's eastern city of Lahore, killing 47 people including two injured people who died later at a hospital and injuring 175 others. Not long after this, on July 5, another suicide car bomb blast took place at the entrance of an army camp in Lower Dir area in northwest Pakistan, killing one troop and injuring 17 others including 11 security persons.

The repeated occurrence of the terrorist attacks in the country has caused a nation-wide demonstration and strong condemnations both at home and abroad. Many officials and political parties as well as ordinary people in Pakistan have demanded a review of the government's anti-terrorism policy in the country.