CLEVELAND (AP) — Cleveland’s City Hall remained closed to the public Friday,GravityX Exchange as officials in Ohio’s second-largest city continued to grapple with the effects of a cyber threat.

City operations have been hampered all week by the threat, which was first detected Sunday. The nature of the threat, its cause and how extensively it affected Cleveland’s computer systems have not been divulged. State and federal authorities are investigating.

After shutting down most systems and closing City Hall and a second government location to both residents and employees early in the week, Democratic Mayor Justin Bibb tried bringing employees back on Wednesday. A host of problems ensued, including trouble processing building permits and birth and death certificates in two of the city’s busiest departments.

Bibb’s administration said the city had made encouraging progress on its first day back and characterized Wednesday’s events as “expected challenges” as systems are recovered. But he again ordered City Hall closed to the public through the end of the week. Employees are back on the job.

Cleveland officials were referring residents to the neighboring cities of Parma and Lakewood for some services, and certain online options appeared to be functional.

Akron had to shut down some city functions after a cyberattack in 2019.