11.   He was injured when the explosive he was carrying went off prematurely.

12.   In March, a small explosive went off at another federal police station in the city, causing minor damage but no injuries.

13.   It was not immediately clear whether the explosives went off prematurely or were detonated by the assailants.

14.   It was not immediately clear whether the explosives went off prematurely or the checkpoint was the intended target.

15.   Last Friday, explosives went off in five banks in the capital, Bogota, causing property damage but no injuries.

16.   One explosive went off next to a school bus and it was not immediately clear if children were hurt.

17.   One teenager was killed, another seriously injured and five others arrested when an explosive they were handling went off in this northern Basque town, news reports said.

18.   On Thursday, a Palestinian man was killed when explosives he was carrying went off prematurely, near a taxi stand in the West Bank town of Hebron.

19.   Police said rocks were thrown near a roadblock and one small explosive went off but no one was injured.

20.   Police were still trying to figure out when the students might have planned for the explosives to go off, he added.