MEXICO CITY — Authorities in the southern Mexico state of Guerrero have stepped up patrols after about 100 schools around the town of Chilapa were forced to close due to gang threats.

Chilapa is in an area where opium poppy and other drug planting is common and it has been plagued by drug gang killings for years. But the situation has become so bad in recent weeks that buses stopped running in the area and schools closed down after teachers and parents reported threats and extortion demands.

The state government said Tuesday that schools are being re-opened on the rural outskirts of Chilapa after security operations involving state police and the armed forces were increased.

Two drug gangs have been fighting turf battles in the area.