Intelligence information gathered by Somali authorities showed that homicide bombers plan to target Mogadishu's airport, seaport and the presidential palace, said police spokesman Abdullahi Hassan Barise.
Members of al-Shabab — a militant group with ties to Al Qaeda — plan to disguise themselves as army generals and carry out the attacks, he said. Barise said officials don't know of a timeframe for the planned attacks.
The warning comes four days after a homicide bomber attacked a university graduation ceremony in Mogadishu, killing 24 people, including three government ministers, medical students and doctors. The government blamed al-Shabab, which has denied responsibility.
The group of protesters — mainly students — took to the streets in the small area of Mogadishu that the transitional government controls, where some shouted slogans against al-Shabab. It was the first such demonstration against al-Shabab, and students taking part could have put themselves at risk of reprisal attacks from the militants.
The protest march — which lasted about 20 minutes — began at the Shamo Hotel, the sight of last Thursday's bombing, and ended a half mile later at Benadir University, the school whose graduation ceremony was attacked.
Somalia has been ravaged by violence since warlords overthrew dictator Mohamed Siad Barre in 1991, then turned on each other. A moderate Islamist was elected president in January amid hopes he could unite the country's feuding factions, but the violence has continued.
Homicide bombings, unheard of in Somalia before 2007, have become increasingly frequent and the lawlessness has raised concerns that Al Qaeda is trying to gain a foothold in the Horn of Africa. The anarchy has also allowed piracy to flourish off the country's coast.