Video | 'Schoolboy' suicide bomber hits army compound in Pakistan, killing 31

The attack took place a parade ground of the Punjab Regiment, inside an enclosed military area of the north-western city of Mardan. A Taliban militant has already come forward with claims that his group had carried out the bombing.

The bomber struck at 0800 (0300 GMT) as recruits were conducting physical training on the parade ground, he said, according to police officials.

According to reports by the BBC, the bomber somehow managed to slip past at least six checkpoints by wearing the uniform of a college located inside the cantonment.

Prime Minister Yusuf Raza Gilani condemned the attack: "such cowardly attacks cannot affect the morale of the security agencies and the resolve of the nation to eradicate terrorism.”

The attack comes only days after a major offensive by authorities against militants in the tribal region of Mohmand, near Mardan during which army helicopter gunships and heavy weapons pounded suspected militant positions.

Mohmand, on the border with Afghanistan, has long served as a sanctuary for the Taliban and al-Qaeda.

Militants have increasingly been using teenage bombers across Pakistan. But in recent times, militants have focused suicide attacks on civilian targets such as places of worship and sporting events.

Speaking to the AFP news agency from an undisclosed location, Taliban spokesman Azam Tariq said the organisation carried out Thursday's attack.

He said he was proud to avenge people killed by US drone attacks and by military operations in the tribal areas, and added that attacks would continue on "those who protect the Americans".

Pakistan's government supported the Taliban when the group was in power in Afghanistan from 1996-2001, but later became an ally of the US when it led an invasion in 2001.

Islamabad denies it is not doing enough to fight the militants, saying it has lost more than 2,400 troops in the war since 2002.