As Kenya mourns the dead of another major attack, Joseph Mullen says western countries must help to tackle the jihadist group in Africa before the danger spreads to their own shores

The massacre of 20-plus civilians by al-Shabaab fighters at a hotel in Nairobi (SAS hero is hailed as Kenyatta orders hunt for hotel terrorists, 17 January) is the third major attack on the Kenyan state within the last five years; two previous being the Westgate shopping mall (71 fatalities) and the Garissa University College (148 fatalities). While the official al-Shabaab explanation is that it is retaliatory action for Kenya’s military intervention in southern Somalia and its participation in Amisom, there is a masking of the broader al-Shabaab strategy. This is to destabilise the states neighbouring Somalia which have Somali-speaking minority populations, in order to establish a sharia-defined east African caliphate.

You report that Kenya’s president said the country would “relentlessly pursue” the planners of the assault. The 2 million-plus ethnic Somali Kenyans (in the Nairobi suburb of Eastleigh, as well as Wajir, Mandera and Garissa counties) may well feel the heavy hand of the Kenyan security forces; the international community should counsel against this, in order not to alienate this important ethnic and religious segment of the Kenyan state.

The threat of al-Shabaab can only be ignored by the west at its peril. It has been described as the world’s largest and most effective jihadist group; almost half of all Islamist-related violence in Africa may be attributed to it, according to the US-based Africa Center for Strategic Studies. Renewed international effort from western countries to support the African Union, Somalia and Kenya in their campaign against al-Shabaab is in effect an extension of their duty of care to their own populations, given the credible level of linked terrorist threat to migrant communities. The Trump administration may also have second thoughts about running down its troop commitment to the Africa Command.

Dr Joseph Mullen

Former UN adviser to Somalia

• Join the debate – email guardian.letters@theguardian.com

• Read more Guardian letters – click here to visit gu.com/letters

• Do you have a photo you’d like to share with Guardian readers? Click here to upload it and we’ll publish the best submissions in the letters spread of our print edition