At least 267 people have died in the latest violence, said the local Elman Peace and Human Rights Organisation, a group that tracks casualties from hospitals, families and counts on the street.
Eighteen civilians and 19 insurgents were killed, it said, and dozens of civilians were injured. There was no way to independently confirm the figures because of the fighting, and the number of Ethiopian and Somali soldiers killed is unknown.
Four days of fighting at the end of March killed at least 1,000 people, mostly civilians.
The government is struggling to gain full control of the capital four months after ousting rival Islamist leaders who ruled much of southern Somalia for the second half of 2006.
Prime minister Ali Mohamed Gedi has said there would be no let-up in the offensive until the government crushed armed resistance by Islamist fighters, backed by foreign jihadists and disgruntled militiamen from the dominant local Hawiye clan.
He blamed neighbouring Eritrea for interfering in Somalia.
"Eritrea is helping with money and military assistance to international terrorists in Somalia," he told a news conference. Eritrean officials have denied such allegations in the past.
Mr Gedi has stressed there is no dispute between the Hawiye clan and his government, saying the fighting is with terrorists linked to al-Qaeda.
An African Union force of about 1,500 Ugandan peacekeepers, working with Mr Gedi's administration and targeted by the insurgents, has so far failed to stop the bloodshed.
Nearly half a million people have fled Mogadishu, thousands sleeping under trees or in the open. The UN has warned of a catastrophe, with diseases like cholera already rife.
- (Reuters)