Mogadishu - The United States government has designated the deputy leader of the Somalia-based al-Shabaab extremist group a "global terrorist."A State Department statement says the designation of Abukar Ali Adan blocks any assets of his that are subject to US jurisdiction and prohibits US citizens from making any transactions with him.The al-Qaeda-linked al-Shabaab is the deadliest Islamic extremist group in Africa. It has been blamed for the October truck bombing in Somalia's capital, Mogadishu, that killed 512 people.Little is publicly known about the reclusive Ali Adan. The US has designated al-Shabaab as a foreign terrorist organisation, and the Trump administration early last year approved expanded military efforts against the group. More than 30 US drone strikes were carried out against al-Shabaab last year.