LONDON — The State Department on Wednesday urged the Nigerian government to investigate reports of a large number of deaths over the weekend in clashes between the military and a Shiite Muslim sect.

The American Embassy in Nigeria said in a statement that the United States was “deeply concerned” about reports of the clashes, which began on Saturday afternoon in the northern city of Zaria.

“While many details of the incidents that reportedly began on Dec. 12 remain unclear, we are dismayed to learn of multiple civilian deaths,” the embassy said in the statement. “It is essential that all sides refrain from actions that further destabilize the situation. The United States calls on the government of Nigeria to quickly, credibly and transparently investigate these events in Zaria and hold to account any individuals found to have committed crimes.”

Representatives of the sect, known as the Islamic Movement in Nigeria, say that up to 1,000 of its members were killed by the military. Military officers say the sect’s members provoked the clash by blocking a convoy carrying the army’s chief of staff, Lt. Gen. Tukur Yusuf Buratai, and that they believed his life was in danger. The military has acknowledged that seven people were killed initially, but it refused to provide updated numbers.

On Wednesday, the Nigerian government said that President Muhammadu Buhari had sent a delegation on Tuesday night to Kaduna State, which includes Zaria, in an apparent effort to defuse tensions.

The delegation, which included Interior Minister Abdulrahman Bello Dambazau and Solomon Arase, the police inspector general, met with the governor of Kaduna State, Nasir Ahmad El-Rufai, and a local emir, Zubair Jibril Mai Gwari.

After the meeting, Samuel Aruwan, a spokesman for the governor, said in a statement that “a situation of calm prevails in the state, with security agencies maintaining a vigilant stance.”

He added: “All residents of the state are requested to promote harmony and peaceful relations, avoid panic and shun rumors.”

The American ambassador to Nigeria, James F. Entwistle, said he believed Mr. Dambazau’s visit to Zaria “was the first step in the timely, transparent investigation,” to which he added that he was sure Mr. Buhari and his administration were committed.

The leader of the Islamic Movement in Nigeria, Sheikh Ibrahim Zakzaky, was detained on Sunday and remains in custody. The Iranian government, which sees itself as a protector of Shiite Muslims worldwide, has demanded that Nigeria conduct an investigation.

The human rights group Amnesty International also called for an investigation into the killings.

“An impartial investigation is urgently needed into these killings,” the group’s Nigeria director, M. K. Ibrahim, said in a statement on Tuesday evening. “Whilst the final death toll is unclear, there is no doubt that there has been a substantial loss of life at the hands of the military. Anyone responsible for unlawful killings should be brought to justice. Those in detention must be granted access to medical care as a matter of urgency and either charged with a recognizable criminal offense or released.”