He is sending 150 state troopers and police staff at the request of Maryland's governor.
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"There is no excuse for the kind of violence we saw yesterday," he said.
State authorities are moving to prevent another night of rioting in Baltimore.
Obama's comments at White House prompted laughter from Prime Minister Shinzo Abe.
"Violence will not be tolerated," Larry Hogan said.
“There are always going to be armchair quarterbacks," said Stephanie Rawlings-Blake.
"This is our city," Anthony Batts said. "Let's make a difference."
The new attorney general condemned the violence and destruction of property.
Gov. Hogan said, "Baltimore City families deserve peace and safety."
The former Maryland governor has canceled the rest of his five-day European tour.