( dpa ) - At least seven people including four Somali policemen have been killed and several others injured in clashes between government troops and Islamist insurgents on Saturday in the capital Mogadishu, witnesses reported. The first clash in northern Mogadishu began at 10 am (0700 GMT) when an Islamist insurgent lobbed a hand grenade at a police patrol, triggering a half-hour battle in which six were killed. One insurgent was killed and three soldiers wounded in another confrontation in Taleeh district, south of Mogadishu. Elsewhere, the government on Saturday implemented a heavy crackdown in two districts in Mogadishu, arresting dozens of people, according to local residents. Meanwhile, 15 people have died and 200 others are in critical condition in a cholera outbreak in Bar Dhere, 344 kilometres north of Mogadishu, according to Ahmed Sharif Hersi, a doctor at Bar Dhere hospital. He called for greater intervention by international aid agencies.