Adamu Adamu, Associated Press
People are treated at the General hospital in Potiskum, Nigeria, Monday, Nov. 10, 2014, following a suicide bomb attack at Government Science Technical College Potiskum. Survivors say a suicide bomber disguised in a school uniform has detonated explosives at a high school assembly in northeast Nigeria, and a morgue worker says 48 students have been killed.

JOHANNESBURG — Nigeria's ambassador to the United States has castigated Washington for refusing to sell "lethal weapons" to fight his country's Islamic uprising, saying the extremists otherwise would have been defeated long ago.

Adebowale Ibidapo Adefuye said the United States is letting down an old ally in its hour of need, and Nigeria's people and government feel abandoned.

"The U.S. government has up till today refused to grant Nigeria's request to purchase lethal equipment that would have brought down the terrorists within a short time," Adefuye told members of the Washington-based Council on Foreign Relations Monday night.

"We find it difficult to understand how and why, in spite of the U.S. presence in Nigeria with their sophisticated military technology, Boko Haram should be expanding and becoming more deadly."

Nigeria's military on Oct. 17 announced an immediate cease-fire with Boko Haram, but the militants have responded with more and deadlier attacks.

Adefuye confirmed that Washington has refused Nigeria's requests because of allegations the defense forces have violated the human rights of Boko Haram suspects. It was not possible to get an immediate response from U.S. officials.

He said the allegations are based on rumors spread by political opponents as Nigeria prepares for February presidential elections.

U.S. laws ban sales of lethal weapons to countries whose military are accused of gross human rights abuses.

An Associated Press investigation found Nigerian troops responsible for the deaths of thousands of detainees since a state of emergency was imposed in May 2013 in three northeastern states.

In the latest such report, community leaders and family members told AP that soldiers raided homes in Potiskum, capital of Yobe state, on Nov. 15 and dragged away young men aged between 18 and 30. Soldiers later dumped 18 bullet-ridden bodies at the hospital mortuary, according to hospital records made available to AP.

The military has not responded to requests for comment.

The executions came two days after a suicide bomber killed 30 people in a procession of moderate Muslims.

On Monday, Potiskum was further terrorized when a suicide bomber killed 48 students at an all-boys high school.