* Local politician says death toll could rise
* Al Shabaab militants claim responsibility
* Government says rebels aim to destabilise strategic town (New throughout, adds comments from al Shabaab, analyst and government)
By Abdi Sheikh and Feisal Omar
MOGADISHU, Oct 19 (Reuters) - A suicide bomber killed at least 16 people on Saturday in an attack on a cafe in a Somali town close to the...