| MARDAN, Pakistan
MARDAN, Pakistan A boy in a school uniform blew himself up at a Pakistani army recruitment center on Thursday, killing 31 cadets, officials said, in an attack that challenges government assertions it has weakened militants.
The army has carried out a series of offensives against the Qaeda-linked Pakistani Taliban, which claimed responsibility for the attack.
Operations in lawless tribal areas along the Afghan border have failed to break the resolve of Taliban fighters determined to destabilize the U.S.-backed government.
The brazen bombing in the northwestern town of Mardan suggested militants are regrouping after a lull in major attacks.
In a sign of how nervous the government is about security, soldiers at the gates of the military compound searched drivers before allowing them to transport coffins inside.
Militant operations in recent months have been mostly sectarian and have not focused on military targets.
"The bomber struck recruits when cadets were busy in their morning training," a military official told Reuters. At least 20 people were wounded.
A military statement said a boy had walked into the compound and blew himself up, without giving his age. An intelligence official said he was 12 years-old but government officials later said he was around 19 or 20 years old.
The Taliban said they had carried out the attack, adding it had targeted recruits because "Pakistani army is working for American interests in Pakistan."
"It seems the Taliban are still a very potent force because they continue to attack installations, even if they have been quiet for a time," said former general Talat Masood.
The Taliban have previously launched bold attacks on the military, nuclear-armed Pakistan's most powerful institution.
Last March, two suicide bombers killed at least 45 people in the city of Lahore, including nine soldiers.
In 2009, Pakistani Taliban militants disguised as soldiers attacked the army's headquarters in Rawalpindi and later took 42 people hostage in a nearby office building.
Prime Minister Yusuf Raza Gilani condemned Thursday's attack at the Punjab Regiment Center.
Gilani's government faces pressure on several fronts.
It is trying to revive a stagnant economy propped up by an$11 billion International Monetary Fund loan which requires politically sensitive reforms.
Public discontent is growing over official corruption, rampant poverty and power cuts.
Washington, the source of billions of dollars in aid, is pressuring Pakistan to intensify its fight against both domestic militant groups and ones that cross the long, porous border to attack Western forces in Afghanistan.
Tensions between the allies are also running high over the case of Raymond Davis, a U.S. embassy employee who killed two Pakistanis in late January.
The U.S. embassy in Islamabad says Davis is a diplomat who acted in self-defense, and that, as he enjoys diplomatic immunity, should be released.
The Pakistanis say it is a matter for the courts to decide, as handing Davis over to the Americans would deepen anti-American sentiment in Pakistan.
(Additional reporting by Zeeshan Haider, Saud Mehsud and Rebecca Conway; Writing by Michael Georgy; Editing by Miral Fahmy)