National Guard troops deployed to head off further rioting in Baltimore on Tuesday as President Barack Obama warned that recent incidents "raise troubling questions" about the policing of black communities.

Violence and looting erupted in Baltimore on Monday after the funeral of 25-year-old African American man Freddie Gray, who died after suffering severe spinal injuries during a police arrest.

Speaking in Washington, Obama condemned the rioting, but also said that a series of recent incidents -- beginning last year with the police shooting of an unarmed teenager in Ferguson, Missouri -- was worrying.

"Since Ferguson... we have seen too many instances of what appears to be police officers interacting with individuals -- primarily African American, often poor -- in ways that raise troubling questions," he said.

Obama expressed sympathy for civil rights leaders and protesters -- as well as for police on the front line of demonstrations -- and said America needed to address the strained ties between officers and blacks.

He said it was important that "we don't just pay attention to these communities when a CVS burns. And we don't just pay attention when a young man gets zshot or has his spine snapped.

"I think there are police departments that have to do some soul searching," he said.

"I think there's some communities that have to do some soul searching. I think we as a country have to do some soul searching. This is not new. It's been going on for decades."

- Reinforcements -

In Baltimore, thousands of military and police reinforcements deployed onto the streets after a night of mayhem saw stores looted, buildings burned, 15 police wounded and 200 suspects arrested.

Maryland Governor Larry Hogan inspected a National Guard barricade on Tuesday and vowed to "make sure what happened last night in Baltimore City is not going to happen again."

"This violence is not going to be tolerated," Hogan told reporters at the temporary checkpoint, manned by riot police and Guard troopers with assault rifles.

"By tonight, you're going to see an overwhelming display of people out there on the streets protecting the citizens."

Baltimore has declared an overnight curfew from 10:00 pm Tuesday (0200 GMT Wednesday), to be in force for a week, and local and national leaders have appealed for calm.

The initial trigger for the violence came after a dignified service for Gray, who died eight days after his spine was all but severed as he was detained by city police.

An investigation has been launched into the cause of his injuries, but many see the incident as only the latest example of police brutality against black suspects.

Gray's family also appealed for calm, but tempers boiled over as young, mainly African American men pelted police with stones and ransacked businesses.

- Distrust of police -

As volunteer clean-up teams took to the streets Tuesday, residents spoke of their terror as gangs roamed the streets fighting police and destroying property.

"It was horrific to the point where my children were actually crying trying to get back to the house because there was so much going on," Latania Graham told AFP.

Many residents condemned the rioters, but also spoke of their distrust of police following incidents of alleged brutality.

Pierre Estep, 56, said officers had held him at gunpoint during a search for drugs when he was only 16 years old.

"He told me he was the next thing to God. He said: 'I'll mess around and take your freedom, or I might mess around and take your life'," Estep told AFP.

Joining many others to express suspicion that the investigation into Gray's death would be a police whitewash, Estep said the situation was getting worse.

"I'm not saying the police have an easy job, but the way they police now… " he said. "I could go on with these horror stories about people living in a black neighborhood."

- Spinal injuries -

Baltimore schools were closed on Tuesday as a safety measure, although some residents worried that this would lead to more restless teenagers on the tense streets.

The Orioles, the city's baseball team, cancelled games against Chicago's White Sox on Monday and again on Tuesday.

The violence is the latest in a series of confrontations between US police and mainly young African American men enraged by what they see as racist attitudes.

Last year's fatal shooting of unarmed teenager Michael Brown by a white police officer in Ferguson triggered coast-to-coast protests.

Lawyers for Gray's family say his death was caused by injuries sustained following his arrest. He lost consciousness in custody and died within a week.

Six officers have been suspended pending the outcome of a police investigation that is to be submitted to state prosecutors by Friday.
Source: AFP