In April 2010, the US adopted Executive Order (EO) 13536, which declared a national emergency in respect of Somalia (namely, for the “deterioration of the security situation and the persistence of violence in Somalia, acts of piracy and armed robbery at sea off the coast of Somalia… and violations of the arms embargo imposed by the United Nations Security Council”). That EO imposed a number of asset freezing measures, including against ‘al-Shabaab’.
In July 2012, EO 13536 was amended by EO 13620, which (inter alia) imposed an import ban on Somalian coal into the US.
Yesterday, President Trump extended those sanctions for 1 year by continuing the national emergency as declared. White House press release here.