Al-Shabab, the Somali armed group, on Saturday threatened to stage more bloody attacks on Kenya after the group's fighters killed nearly 150 people during an assault on a Kenyan university on Thursday.

In the message, directed at the Kenyan public, the group vowed a long and gruesome war, saying Kenya's cities will ‘run red with blood’.

Four masked al Shabaab gunmen went on a killing spree in a pre-dawn raid, hunting down and executing students in a college campus in Garissa, a northeastern town about 200km (120 miles) from the Somali border.

The al Qaeda aligned group said the attack was retribution for Kenya's presence in Somalia and mistreatment of Muslims within Kenya.

‘No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath from occurring in your cities,’ the group said in an emailed statement.