WASHINGTON, Nov. 24 -- The U.S. Department of Justice will continue investigating the death of African American youth Michael Brown in Ferguson, Mo., and the Ferguson Police Department, U.S. Attorney General Eric Holder said Monday evening.

"While the grand jury proceeding in St. Louis County has concluded, the Justice Department's investigation into the shooting of Michael Brown remains ongoing," Holder said in a statement in the wake of a grand jury's decision not to charge Darren Wilson, the white police officer of the Ferguson Police Department, in the fatal shooting of the unarmed teenager in August.

"Though we have shared information with local prosecutors during the course of our investigation, the federal inquiry has been independent of the local one from the start, and remains so now," Holder said, urging federal prosecutors to avoid prejudging any of the evidence and resist forming premature conclusions.

The department will continue to investigate "allegations of unconstitutional policing patterns or practices" by the Ferguson Police Department, he added.

Holder said Brown's death was "a tragedy" and this incident "has sparked a national conversation" about the need to ensure confidence between law enforcement and the communities they protect and serve.

In a statement from the White House earlier Monday night, U.S. President Barack Obama also said "this is not just an issue for Ferguson, this is an issue for America", adding that he had instructed Holder to work with cities across the country to help build better relations between communities and law enforcement.

"While constructive efforts are underway in Ferguson and communities nationwide, far more must be done to create enduring trust," Holder said, appealing for calm and peaceful protest in response to the grand jury's decision.

About 200 protesters demonstrated peacefully outside the White House on Monday night, holding signs reading "Justice for Michael Brown". But hundreds of people gathering outside the Ferguson police station reacted with anger and dismay when heard of no indictment for Wilson.

"In the coming days, it will likewise be important for local law enforcement authorities to respect the rights of demonstrators, and deescalate tensions by avoiding excessive displays...," said Holder.