Police used mine detectors Saturday to check cars arriving at a Pretoria rugby stadium as part of tightened security measures following a series of bombings.

A mine attached to a telephone pole exploded outside the clubhouse of a field hockey team in a Johannesburg suburb. No serious injuries were reported.At a rugby match in Cape Town, a police helicopter circled the stadium.

Last weekend, a car bomb exploded outside a Johannesburg stadium as spectators left a rugby match. Two people died and 35 were injured. Other recent targets included a video game arcade and a beachfront restaurant.

On Saturday, a large police contingent was on duty at Pretoria's main rugby stadium. Spectators arriving for the game were searched as they entered the grounds, and mine detectors were used to scan underneath vehicles entering parking lots.

Police have blamed the recent bombings on the outlawed African National Congress guerrilla movement, which has not commented on the bombings. The ANC is the main group fighting to overthrow South Africa's government.

Authorities across the country have launched a "bomb awareness campaign" to encourage greater public vigilance. City officials in Johannesburg are publicizing a special emergency telephone number to be used for reporting suspected bombs, and the Cape Town Chamber of Commerce has published a set of security guidelines to shopowners.