CONAKRY, July 12 (Reuters) - Gunmen opened fire on a vehicle carrying two government ministers in Guinea, injuring a woman passenger in what police said on Thursday they believed was an attack by criminals. The ambush occurred late on Wednesday when the car carrying Justice Minister Paulette Kourouma and Social Affairs Minister Hadja Tete Nabe was passing near the village of Timbo, more than 300 km (180 miles) northeast of the capital Conakry. Police and witnesses said the ministers' bodyguards returned fire and one of the attackers, believed to be local highway robbers, was captured. Another woman in the car was wounded. "The bullets shattered the windscreen of the vehicle in which the ministers were travelling," a senior police officer, who asked not to be named, told Reuters. An investigation into the shooting had begun. Following nationwide anti-government riots in January and February that swept across Guinea, the world's leading exporter of the bauxite from which aluminium is made, attacks by armed bandits have increased sharply. Clashes between security forces and the rioters killed 137 people, mostly unarmed demonstrators, and many rural prefects and governors fled from their posts in the interior. Prime Minister Lansana Kouyate, a diplomat who was appointed in February under a deal to end the strikes and rioting against the rule of ageing President Lansana Conte, has been trying to restore public order and revitalise the struggling economy.