...Outgoing U.S. Department of Homeland Security Secretary Jeh Johnson said police aim to separate groups to diffuse tensions, similar to last-year's political conventions.

"The concern is some of these groups are pro-Trump, some of them are con-Trump, and they may not play well together in the same space," Johnson said on MSNBC on Thursday.

About 28,000 security personnel, miles (kilometers) of fencing, roadblocks, street barricades and dump trucks laden with sand will be part of the security cordon around 3 square miles (almost 8 square km) of central Washington.

About 30 groups that organizers claim will draw about 270,000 protesters or Trump backers have received permits for rallies or marches before, during and after the swearing-in. More protests are expected without permits.

A protest group known as Disrupt J20 has vowed to stage demonstrations at each of 12 security checkpoints and block access to the festivities on the grassy National Mall....