During her seven-country tour, Clinton highlighted the continent's successes, stressed the work yet to be done, and strengthened US trading alliances.
The brazen attack spotlights the presence of religious foreigners in a lawless country that US officials say could soon turn into the next terrorist haven run by militant Islamists.
Clinton met with Somalia's president Thursday and traveled to Tshwane (Pretoria) Friday. She must work with a continent most united by a desire to appear independent from the US.
In Kenya, she expressed dismay over rejection of human-rights tribunal – but emphasized shared trade and security interests.
One aim: to bolster relations with resource-rich countries where China has been aggressively extending its presence.
Police say the four Australian citizens had received training in Somalia and were planning to attack a military barracks in Sydney.
Tuesday, battles between government forces and Islamist militias in Mogadishu killed seven civilians. Experts say some of the militias might be open to dialogue with President Sharif.