Somalia ? A masked man hurled a grenade into a busy market Thursday in Mogadishu, setting off an explosion and gunbattle that killed four people, witnesses said.

The government imposed a nightly curfew following a week of bloodshed.

Starting today, anyone outside their homes between 7 p.m. and 5 a.m. will be arrested, said Gen. Mohamed Warshame Darwish of Somalia’s intelligence service. At least 10 people have been killed since Monday.

The grenade was thrown at police at the Bakara Market. Four people were killed in the explosion and gunbattle that followed.

Police sealed off the market, which also houses Mogadishu’s weapons dealerships. The government had ordered weapons dealing to stop months ago, but vendors took their business underground.

Government and allied Ethiopian forces have been battling insurgents and clan militiamen since driving out an Islamic movement from Mogadishu six months ago. More than 1,000 civilians have been killed and hundreds of thousands have been displaced.