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.
The curfew takes effect Tuesday night and will last at least a week, the mayor said.
"We call for peaceful protests so that additional lives are not lost," said Rep. Butterfield.