LIMA, May 19 (Reuters) - A backpack full of dynamite exploded in a crowded market in southern Peru, killing six people and wounding at least 50, police said on Saturday.

Police said they were trying to work out if the blast was the result of an attack or an accident.

The explosion tore through the market in the city of Juliaca, 825 miles (1,330 km) southeast of the capital, Lima, at about 10 p.m. on Friday (0300 GMT on Saturday).

Some 1,000 people were in the market celebrating the anniversary of its opening over 40 years ago.

In the initial aftermath, the head of the local police force, Raul Becerra, said the blast was caused by fireworks intended for the celebrations.

"This is an irresponsible and accidental consequence of people drinking alcohol," he told Peruvian radio station RPP.

Police sources later told Reuters they had not ruled out the possibility of a bomb attack.

Shining Path, the Maoist rebel group that plunged Peru into violence during the 1980s and 1990s, marked the 27th anniversary of its foundation this week.

Although it has been largely defeated, the group still carries out occasional guerrilla attacks.

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