(CNN) -- Two days of fighting between government and Ethiopian troops and Islamic militants in Somalia's capital, Mogadishu, left 81 civilians dead and more than 100 wounded, a local human rights group reported Sunday.
Sudan Ali Ahmed, the head of the Mogadishu-based Elman Human Rights Group, accused the rebels of using civilians has human shields, while the transitional government's Ethiopian allies shelled residential neighborhoods with tanks and artillery.
"We are condemning the warring sides in the strongest terms for violating human rights and committing war crimes against civilians," Ahmed said.
Large numbers of civilians have been fleeing two neighborhoods in the northeastern part of the capital where the fighting has been taking place, witnesses reported, joining a population of displaced Somalis that aid groups estimate already tops 1 million.
A witness told CNN that Ethiopian troops seized a mosque in one of the neighborhoods where the worst fighting was taking place. The Ethiopians left the bodies of six elderly men outside the mosque around noon Sunday and were separating men and boys from the neighborhoods and arresting them, the witness said.
"The Ethiopians are firing heavy weaponry into areas where civilians are heavily populated, while the Islamic militants are firing mortars and RPGs [rocket-propelled grenades] from within those areas," Ahmed said. "So the exchange is causing a civilian casualty toll which is unspeakable."
Others, like Mohamed Ismaail Ali, a father of eight in the capital's Suqa Holaha neighborhood, reported being trapped by the fighting. Ali said he could see three bodies through his window.
"This morning, we have had a plan to flee from our house after yesterday's clashes," he told CNN. "But it became totally impossible to go outside the house, because artillery is falling everywhere, let alone the straying bullets which are flying any minute."
Residents at Darimoole, a village on the road linking northeastern Mogadishu to the neighboring town of Bal'ad, told CNN that a new exodus of people has begun.
"The people are fleeing in a large number as earlier 2007, when first rounds of fighting between the Ethiopians and the Islamic militants happened in the capital," said Omar Hagi Ali, an elder at Dirimole.
Somali Prime Minister Nur Hassan Nur Ade had no immediate comment on the latest fighting, the latest in a lengthy insurgency against his government and its Ethiopian backers.
Ethiopia invaded Somalia in December 2006 to install the U.N.-backed transitional government in Mogadishu after a decade and a half of near-anarchy. Ethiopian troops quickly routed the provisional government set up by the Islamic Courts Union, which had wrested control of the capital from Somali warlords six months earlier.
The Islamists responded by launching a guerrilla war that destroyed Ethiopia's plans for a quick withdrawal. A year after the invasion, Ethiopia's government appealed for international contributions to a peacekeeping mission that was supposed to replace its forces, but the African Union-led mission has drawn few takers.
The invasion had the blessing of the United States, which accused the ICU of harboring suspected al Qaeda operatives -- including men believed to have planned the 1998 bombings of U.S. embassies in Kenya and Tanzania. The ICU denied the allegation, but the insurgency its fighters launched against Ethiopian troops won the praise of al Qaeda's fugitive leaders.