SOMERVILLE, Mass. — Dozens of police officers and emergency medical workers from across Massachusetts gathered here on Thursday to protest a “Black Lives Matter” banner at City Hall, making this largely white, working-class suburb of Boston the latest flash point in the escalating national tensions between the police and advocates of the Black Lives Matter movement.

The police were protesting the decision by the city’s mayor, Joseph A. Curtatone, to keep the banner hanging on outside City Hall. The police contend that the banner is divisive and gives voice to a movement that has inspired violence against the police, including the recent killing of officers in Dallas and Baton Rouge, La.

“Because some elements identified with the ‘Black Lives Matter’ movement have resorted to killing innocent police officers and putting the lives of citizens in jeopardy, the Massachusetts Municipal Police Coalition cannot stand for the continued display of that organization’s banner on a public building,” Michael McGrath, an officer of the coalition and the president of the Somerville Police Employees Association, told the crowd.

As he spoke, officers from two dozen nearby cities and towns, wearing street clothes, stood quietly around him, and television helicopters hovered overhead. The police unfurled a large blue banner that read “Cops Lives Matter” and held posters saying “Support Your Local Police.” About 100 residents looked on.