Anti-police-violence protesters block Boston-area highway

Police detain a protester who was part of a group who blocked southbound lanes of Interstate 93 during the morning rush hour in Somerville, Massachusetts, Jan. 15, 2015.

Reuters/Brian Snyder

Last Updated Jan 15, 2015 11:24 AM EST

BOSTON -- Boston-area highway lanes were blocked Thursday by activists protesting what they call "police and state violence against black people." Police have reopened all of the lanes.

State police shut down Interstate 93 north-bound at East Milton Square south of the city, and I-93 south at Mystic Avenue north of the city at the height of the morning commute Thursday, inconveniencing thousands of drivers.

The southbound lanes were reopened at about 8 a.m. and the northbound lanes at about 10 a.m.

State police say 29 protesters, some of whom chained themselves to concrete-filled barrels, had been arrested.

The Boston contingent of Black Lives Matter said in a statement that the protest was intended "to confront white complacency in the systemic oppression of black people in Boston."

Boston Mayor Martin Walsh called the protest dangerous.