Nigerian security forces killed at least 23 people in the north eastern city of Maiduguri in retaliation for a bomb attack blamed on a radical Islamist sect, Amnesty International said on Monday.
Boko Haram, a radical group which wants sharia law more widely applied across Africa's most populous nation, has been behind almost daily shootings and attacks with homemade bombs in and around Maiduguri, the capital of Borno state.
Saturday's attack near a market in the centre of the city injured three soldiers and killed several civilians, authorities and witnesses said.
Maiduguri residents have accused members of a military Joint Task Force (JTF) of using indiscriminate force when reacting to attacks carried out by Boko Haram. The government says there have only been isolated incidents of misbehaviour by officials.
"House to house searches, brutalisation, unlawful arrests, killings and disappearances have been the operating practice in Maiduguri for some months now," said Tawanda Hondora, Amnesty International's Deputy Director for Africa.
"Unless steps are taken to ensure security forces operate within the law and respect human rights at all times, the next time Boko Haram attacks or kills a soldier, we are likely to see the same thing happen again," Hondora added.
Thousands of people have fled Maiduguri, the capital of Borno state, in recent weeks, fearing being caught up in clashes between JTF officials and Boko Haram.
More than 250 people have been killed since July 2010 by people believed to be members of Boko Haram, Amnesty International said in a press release on Monday. Attacks usually target police, churches and outdoor drinking areas.
Bomb blasts in the north have replaced militant attacks on oil facilities hundreds of kilometres (miles) way in the southern Niger Delta as the main security threat in Nigeria. The United States and European Union have condemned the violence.
Boko Haram strikes have spread farther afield in recent months, including a bomb in the car park of national police headquarters in the capital, Abuja, last month.
The group's views are not espoused to by the majority of Nigeria's Muslim population, the largest in sub-Saharan Africa