CHICAGO (CBS) — Police are warning CTA riders after a series of robberies in the Loop.

The offenders conducted three robberies on CTA trains, platforms or nearby sidewalks along State Street last week.

The robbers, a group of African-American men between 17- and 20-years old, “used force to go into the victim(s) bags and pockets and removed the victim’s personal property,” according to a community alert from police.

The robberies happened:

In the 0-100 block of South State Street on May 28 at 3:00 a.m.
In the 500 block of North State Street on May 29 at 2:40 a.m.
In the 100 block of North State Street on May 29 at 2:30 a.m.

Police are connecting another robbery in 2400 block of West Montrose Avenue on May 29 at 6:00 a.m.

Police are reviewing video and pics from cameras on CTA property.