FBI agents have searched the office of an Ohio group that supports voter registration efforts, seizing documents and computer files, a board member of the organisation said Friday (June 12).

It's the latest action by the Trump administration connected to voting or election operations in the states, and it comes in a state that is expected to have hotly contested races this fall for governor and US Senate.

Federal agents showed up at the Cleveland office of the Ohio Organizing Collaborative on Thursday and spent hours questioning staff, said Prentiss Haney, a board member of the grassroots organisation. The organisation was founded in 2007 and describes its mission as fighting for criminal justice reform, racial justice and an expansion of voting rights.

Federal agents also went to the homes of people who have worked with the organisation, seeking interviews and information about alleged voter fraud, Haney said. He accused the agents of "intimidation tactics and harassment" and expressed concern that the investigation was designed to sow doubt in the coming elections.

The focus of the probe was unclear, but a person familiar with the matter said Friday that investigators were examining potential fraud violations. The person was not authorised to speak publicly about the investigation and spoke on the condition of anonymity.

The Justice Department declined to comment on Friday, and a spokesperson for the FBI in Cleveland did not respond to messages seeking comment.

To obtain a search warrant, federal authorities must convince a judge that probable cause of criminal activity exists. Though the information authorities presented was not immediately released, Democrats expressed skepticism about the basis of a search that unfolded against persistent concerns of a politicized FBI and Justice Department.

The party's nominees for the state's top races issued statements Friday saying they were troubled by the FBI raid.

"Any attempts by federal law enforcement to intimidate eligible Ohioans from registering to vote are unacceptable," said Dr. Amy Acton, the state's former public health director, who won the state's Democratic primary for governor and is challenging Republican Vivek Ramaswamy.

Democrat Sherrod Brown, who is challenging Republican Sen. Jon Husted in the fall, called on the FBI to make public "any and all activities around these raids."