Ugandan police say they have arrested 20 people suspected of collaborating with Islamist militants believed to have attacked a school last Friday. 

The head teacher and school's director are among the detained. 

Forty-two people - mostly students - were killed at Lhubiriha Secondary School in Mpondwe in western Uganda.

Many were burnt to death in their dormitory.

The Ugandan army is still hunting Allied Democratic Forces (ADF) militants, who have reportedly moved back over the border into eastern Democratic Republic of Congo where they are based.