WASHINGTON - A report by the Federal Bureau of Investigation (FBI) found that 50 active shooter incidents took place in the country in 2016 and 2017, 10 more than in the previous two-year period.

The figures from the FBI report put the United States on a steadily growing trend of active shooter incidents, which the FBI describes as "one or more individuals actively engaging in killing or attempting to kill people in a populated area".

According to the report, dated April 2018 and reported by US media on Monday, the 50 active shooter incidents took place in 21 states across the country, killing 221 and wounding 722.

Twenty cases met the "mass killing" criteria, which means three or more are killed in one incident.

The most deadly active shooter incidents over the past two years include the Las Vegas shooting in October 2017, which killed 58, as well as the Orlando nightclub shooting and the Texas church shooting.

Broken down by state, Texas, a conservative state with lax gun regulations, topped the chart with six cases. California and Florida followed with five cases. Other states high on the list include Ohio, Maryland and Washington.

During the 2014-2015 period, 40 such incidents caused 231 casualties across the country.