Sharmarke's announcement came after heavy shelling between Somali troops and anti-government fighters near the presidential palace left 12 people dead on Sunday.
Much of the fighting was concentrated in Mogadishu, witnesses said.
A day ealier, 23 people had been killed and 51 injured on Saturday in clashes between the two sides.
"It was a very gruesome scene," a local resident said.
He saw dead bodies and wounded people running away from the scene on Sunday.
Ali Adde, deputy-director of Madinah hospital in Mogadishu, said that they had received 31 patients with serious injuries.
"The hospital is overcrowded with injured people," he said.
Somali forces and the anti-government fighters, who want to instal an Islamic state in Somalia, blamed each other for sparking the violence.
A surge of violence that erupted in Mogadishu in May has killed about 200 people and forced tens of thousands to flee the capital.
Somalia has been without an effective government since 1991 when the overthrow of the government at the time plunged the country into chaos.
A UN-backed government is currently in place in Mogadishu, but it is struggling to restore order with anti-government fighters controlling large patches of the country.