WASHINGTON (AP) — New FBI data show violent crime in America rose for the second year in a row in 2016. The numbers suggest the increase was driven by a spike in killings in some major cities.

The Trump administration seized on the data as proof of the legitimacy of its tough-on-crime agenda. Attorney General Jeff Sessions has said rising crime warrants the need to return to tougher tactics like more arrests and harsher punishments for drug criminals.

But criminologists cautioned the new numbers may not show the start of a long term trend.

Violent crimes such as shootings and robberies rose 4.1 percent in 2016 from the year before. And the data says homicides climbed 8.6 percent.

Experts are divided about the causes of the rise and about how to respond.