At least 31 people killed in blast in Pakistan

At least 31 people were killed and 50 wounded when a bomb hidden in a carton of vegetables ripped through a crowded marketplace in Pakistan's restive northwestern tribal region Friday, officials said.

The attack took place during the regular Friday bazaar in Kalaya, a town in a Shiite-dominated area of Orakzai tribal district.

"According to our initial investigation, it was an improvised explosive device hidden in a carton of vegetables," said an official.

A senior official, Ameen Ullah, said 31 people had been killed, including 22 Shiites.

More than 50 people were wounded, with 17 of them in critical condition, he said. Tribal police confirmed the toll.

Orakzai is one of seven restive semi-autonomous tribal regions on the Afghan border, an area that has long been a focal point in the global war on terror and was famously described by Barack Obama as "the most dangerous place in the world".

Washington has insisted that the mountainous region provides safe havens to militants including the Afghan Taliban and Al Qaeda -- an allegation that Islamabad denies.

Pakistan, which joined the US war on terror in 2001, says it has paid the price for the alliance.

It has been battling Islamist groups in the tribal belt since 2004, after its army entered the region to search for Al-Qaeda fighters who had fled across the border following the US-led invasion of Afghanistan.

Multiple bloody military operations have been carried out in the area, officially known as the Federally Administered Tribal Areas (FATA) and home to around five million ethnic Pashtuns.

Security has improved in the region in recent years, though lower-level attacks are still carried out with devastating regularity, often targeting Shiites in the area.

But it remains notorious for the availability of cheap guns and smuggled goods, along with narcotics including hashish and opium grown in both the FATA and neighbouring Afghanistan.

Residents also complain of undue harassment by security forces, citing disappearances and extrajudicial killings.

Earlier this year Pakistan passed legislation which paves the way for the tribal areas to be merged into neighbouring Khyber Pakhtunkhwa province, bringing them into the political mainstream.

The move will impose the Pakistani judicial system on a region still loosely governed by British colonial-era laws and the tribal system of honour, and which has always existed on the fringes of the state.