MEXICO CITY, Aug. 1 (Xinhuanet) -- Explosions hit a horse racing track in mid-west Mexico early Monday, killing four people and injuring at least 20 others, police said.

    The incident occurred in the pre-dawn hours in Tonala where about 300 kilometers to the west of this capital city.

    It was unclear what caused the explosions, but reports quoted police in Tonala as saying that they found remains from two exploded grenades.

    Six people were arrested while they were trying to rescue one of the injured from a hospital, police said. Enditem