Lagos, Nigeria (CNN) -- More than 30 people have been shot dead in Nigeria, the head of Amnesty International said Friday, only a day after the rights group accused Nigerian security forces of committing serious abuses in their efforts to crack down on the militant Islamist group Boko Haram in the region.
The latest deaths occurred in the town of Maiduguri, in Borno state, which has been the scene of much of the violence as Boko Haram seeks to impose a strict version of Sharia law in the Muslim-dominated northern part of the country.
Amnesty International Secretary General Salil Shetty said: "We have certainly confirmed from our contacts that over 30 people have been killed -- summary executions, we understand; bodies found in the morgue."
Witnesses told Amnesty and CNN that security forces from the Joint Task Force, or military, carried out the killings.
"These are not isolated examples -- it's happening all the time," Shetty added. "Ordinary citizens are simply caught in the crossfire."
Shetty appealed for the government to ensure the rule of law was followed by its own forces in tackling the militant groups.
"There's no way in which we can improve the security situation in the north, which we all want ... by increasing insecurity," he said. "We cannot improve human rights by taking people's lives and for security forces to be themselves beyond the pale of the law is just simply unacceptable."
Lt. Col. Sagir Musa, a spokesman for the Joint Task Force, told CNN that the reported killings are under investigation.
"JTF doesn't condone or encourage infractions or indiscipline and where that happens we immediately visit sanctions accordingly," Musa said.
Meanwhile, the military blamed Boko Haram for killing retired Major Gen. Muhammadu Shuwa and a guest in Maiduguri Friday.
Four gunmen entered Gen. Shuwa's house and opened fire on him and his guests, Nigerian military spokesman Lt. Col. Sagir Musa said in a statement. Nigerian troops located in the area immediately cordoned off the area and are searching for the assailants, he said.
In its report Thursday, Amnesty International condemned the increasingly brutal attacks carried out by Boko Haram since 2009, but said Nigeria's security forces "have perpetrated serious human rights violations" in their response.
"Hundreds of people accused of links to Boko Haram have been arbitrarily detained without charge or trial; others have been extrajudicially executed or subjected to enforced disappearance," the report said.
"At the same time, the Nigerian government has failed to adequately prevent or investigate the attacks or to bring perpetrators to justice; and victims have not received prompt and adequate reparation and remedy.
"The cycle of attacks and counterattacks has been marked by unlawful violence on both sides with devastating consequences for the human rights of the people trapped in the middle."
A spokesman for the Nigerian military, Col. Mohammed Yerima, rejected the allegations made in Thursday's report.
"We sincerely disagree with the report released by Amnesty International," he told CNN. "We believe that their statistical data is unfounded. They didn't interview anybody from Boko Haram, and they didn't interview us; they seemed to have just spoken to people on the street."
He also dismissed allegations made in the report that the military participated in extrajudicial killings of suspects or used torture during interrogations.
"We deny that. What would we gain from killing people like that? We don't torture, we interrogate. If they are found not to be members of Boko Haram, we release them immediately, take them back to where we picked them up and we apologize," he said.
Amnesty International said it had shared its findings with the Nigerian authorities before it published the report, as well as requesting further information on certain cases, but that it had received no response.
Its researchers met with senior government officials, including the ministers for police affairs, justice and the interior, and the defense headquarters representative, the rights group said.
Amnesty International also acknowledged the challenges faced by under-resourced police in the face of militant activity, and said the attacks by Boko Haram targeting civilians "may constitute crimes against humanity."
Over the past three years, Boko Haram has waged a violent campaign of bombings of Christian churches that have killed hundreds and wounded many more. There have been fewer attacks by Christian militant groups.
Nigeria has almost equal numbers of Christian and Muslims, with the south predominantly Christian.
Boko Haram and other Muslim groups claim the north has been starved of resources and marginalized by the government of President Goodluck Jonathan, a Christian.
CNN's Laura Smith-Spark and Nana Karikari-apau contributed to this report.