A grenade attack in a public market has wounded 21 people in western Rwanda, police said on Wednesday, according to Reuters. Police spokesman Theos Badege said four of those wounded on Tuesday evening in Rusizi district were in a serious condition. \"Right now we can\'t say the motive of the attack. We haven\'t arrested anyone as yet but security organs have intensified investigations,\" Badege said. Rwanda\'s capital was hit by a string of grenade attacks last year, which the government blamed on two high-ranking army officers now in exile.