Missouri police have clashed with protesters in St Louis after an officer shot dead a black teenager close to where another black youth, Michael Brown, was killed in August sparking national protests.
A crowd of about 100 gathered at the scene in St Louis early on December 24 after scuffles the night before.
Police said the man who was shot, Antonio Martin, 18, had pointed a gun at the police officer.
For weeks there have been widespread protests over alleged police brutality.
Berkeley is about 2 miles from the St Louis suburb of Ferguson, where 18-year-old Michael Brown was shot dead by a white officer.
St Louis County police chief Jon Belmar said a police officer was responding to a call about a theft when he saw Antonio Martin and another man at a petrol station in North Hanley Road and approached them.
He said that Antonio Martin pointed a handgun at the officer, and the officer responded by firing three shots. One of the shots hit Antonio Martin, he said.
The officer “responded with what he thought was commensurate force at the time”, Col. Jon Belmar said, adding that “most of us would feel in imminent danger of losing our lives at that point”.
Col. Jon Belmar described the incident as “a tragedy for everybody”, and said a prosecutor had been assigned to investigate the case.
“Our hearts certainly go out to the family, but bad choices were made,” he added.
“This individual [Antonio Martin] could have complied with the officer; he could have run away; he could have dropped the gun. Things did not have to end with him approaching an officer with a 9mm pistol in his hand.”
Berkeley Mayor Theodore Hoskins said that both the city and St Louis County would hold independent investigations.
The incident could not be compared with the shooting of Michael Brown in Ferguson, Theodore Hoskins said, adding: “The video shows that the deceased pointed a gun… at the officer.”
Between 200 and 300 people gathered at the scene after the incident, Col. Jon Belmar said, adding that bricks were thrown at police officers, and three explosive devices set off.
Four people had been arrested for assaulting police officers, he said.
Police are releasing video footage of the run-up to the shooting, and an image of the second man, who fled the scene.
The handgun said to belong to Antonio Martin has been recovered by police.
The National Guard has been sent to the town of Ferguson as protests escalate over the police shooting of black teenager Michael Brown.
Missouri Governor Jay Nixon signed an order to “help restore peace and order and to protect the citizens of Ferguson”.
The decision was made as police clashed with angry crowds shortly before a second night under curfew began.
Police in Ferguson, a suburb of St Louis, said they came under attack and had “no alternative” but to respond.
Captain Ron Johnson said protesters had thrown Molotov cocktails and bottles at security forces, and set up barricades before the five-hour curfew began at midnight on Sunday.
“For those who would claim that the curfew was what led to [the] violence, I will remind you this incident began three and a half hours before the curfew was to have started,” Ron Johnson told journalists in Ferguson on Monday.
Correspondents at the scene described seeing smoke clouds rise up as police began to disperse the protests on West Florissant Avenue, with a helicopter beaming down a spotlight.
Some of the demonstrators were spluttering and poured bottles of water into their eyes as they felt the effects of tear gas. Others sought cover from the unrest inside a fast food restaurant.
The killing of Michael Brown by a white policeman in a street on August 9 has inflamed racial tensions in the largely black suburb.
The National Guard has been sent to the town of Ferguson as protests escalate over the police shooting of black teenager Michael Brown (photo AP)
Officer Darren Wilson shot Michael Brown after reportedly stopping him for walking in the street, disrupting traffic.
Governor Jay Nixon has criticized police for releasing surveillance video which apparently shows Michael Brown stealing some hours before his death.
Jay Nixon said the release of the footage “appeared to cast aspersions” on the dead man, saying “it made emotions raw”.
He also condemned the protesters: “These violent acts are a disservice to the family of Michael Brown and his memory and to the people of this community who yearn for justice to be served and to feel safe in their own homes.”
A preliminary post-mortem examination by the St Louis County Medical Examiner’s office on the day after Michael Brown’s death found he had been shot, police said, without disclosing how many times.
However, a preliminary private post-mortem report has since revealed that he was shot at least six times, including twice in the head, the New York Times reports.
The bullets did not appear to have been fired from very close range due to the lack of gunpowder on the victim’s body, forensic pathologist Michael Baden was quoted by the paper as saying.
Michael Baden flew to Missouri on Sunday to conduct a separate autopsy at the request of the family.
Officials last week confirmed that Darren Wilson was a six-year police veteran with no previous complaints against him. He has been on paid administrative leave since the shooting.