ISLAMABAD, Jan 2 (Reuters) - Pakistani authorities published on Wednesday photographs of a severed human head and two men standing in a crowd moments before Benazir Bhutto was killed and offered a reward for their identification.

Opposition leader and former prime minister Bhutto was killed in a gun and suicide-bomb attack as she left a rally in the city of Rawalpindi last Thursday.

One of the pictures, published in a notice in Pakistan's biggest Urdu-language newspaper, shows two men standing in the crowd outside the Bhutto rally moments before she came out and was killed.

The picture, already published by a television station, shows a clean-shaven young man wearing sun glasses, a white shirt and dark waist coat.

Behind him stands a man with a white shawl over his head, who a television station said was believed to be the bomber.

Later pictures and video footage have shown the young man firing a pistol at Bhutto as she left the rally standing up through the sunroof of her land cruiser to wave to supporters.

A second photograph published in the notice on Wednesday shows a severed human head, apparently that of the suicide bomber.

"People are requested to extend help in the arrest of the perpetrators of this terrible incident," Punjab province's interior ministry said in the notice. Rawalpindi is in Punjab.

It offered a reward of 10 million rupees ($164,000) for information leading to their identification.

The government has not said how many attackers it believes were involved but has blamed an al Qaeda-linked militant based on the Afghan border, Baitullah Mehsud.

But many Pakistanis believe others from among Bhutto's old enemies, perhaps from within the powerful security agencies, were involved.

A spokesman for Mehsud denied involvement.

Apart from the question of who was behind the attack, controversy has been raging over the exact cause of Bhutto's death.

The government says Bhutto was killed when she fractured her skull on the lever on a sunroof of her car during the attack.

Bhutto's supporters say she was shot.

Video footage shows the clean-cut young man firing at least three shots at Bhutto from a distance of about 10 feet (3 metres), her white shawl appearing to move, perhaps as a bullet struck, and her dropping back into her armoured vehicle. (Reporting by Zeeshan Haider; Editing by Robert Birsel)

AlertNet news is provided by