(Update) Black Lives Matter Boston protesters arrested after clogging I-93

In a show of solidarity with the recent racial outrage over the killings by U.S. police of unarmed black men, protesters from the Boston chapter of Black Lives Matter on Thursday blocked traffic on Interstate 93, in both directions, snarling the morning commute.

Two groups of protesters chained themselves to 1,200 pound barrels in the middle of the highway. The protesters delayed traffic near East Milton Square in Milton and in Medford, Massachusetts State Police said.

PHOTOS:I-93 protest photos show police arresting demonstrators

According to State Police, a total of 29 were arrested. More information is expected to be released at an 11:45 a.m. press briefing.

The barrels were filled with cement, according to organizers. Police used chainsaws to separate the protesters from the barrels.

The demonstration caused a “serious risk to public safety,” State Police said.

By 9:20 a.m., only one lane was open on the southbound side of the interstate in Milton, while the northbound side remained totally closed. State Police first reported the protests before 8 a.m.

Black Lives Matter Boston, a local chapter of the national Black Lives Matter organization, has said it organized the protest to demonstrate against “police and state violence against black people.”

“Our nonviolent direct action is meant to expose the reality that Boston is a city where white commuters and students use the city and leave, while black and brown communities are targeted by police, exploited, and displaced,” said organizer Katie Seitz, in a statement.

Violent protests broke out across the nation late last year after grand juries in New York and Missouri declined to bring criminal charges against white police officers in the killing of unarmed black men.

Morgan Rousseau contributed to this story.

Here’s some tweets from police about the protest:

Protestors with arms chained together inside barrel on Rte 83 Milton pic.twitter.com/ORaUqQ7les
— Tim Alben (@TimAlben) January 15, 2015

#Protest all you want…Do not block hwy, it’s illegal.
Stopping highway traffic proves nothing. What if an ambulance needs to get by?
— Dustin Fitch (@DustinGFitch) January 15, 2015

Call work, ur gonna be late.
If you can seek another #MAtraffic route, do it! If u are stuck on 93, we are doing our best with what we have
— Dustin Fitch (@DustinGFitch) January 15, 2015