BEIJING, Nov. 27-- Residents in Ferguson, a suburb of St. Louis County in the central state of Missouri, are hoping for a calm night before Thanksgiving Day, as protests over the acquittal on the murder charge of a white policeman who shot dead an unarmed black teenager have spread to other U.S. cities.

Protests have taken place in about 170 U.S. cities including Boston, Los Angeles and New York and at least 196 people have been arrested since a grand jury decided Monday not to indict white officer Darren Wilson in the Aug. 9 shooting death of 18-year-old Michael Brown.

The case touched off a debate about race relations in the United States and even inspired rallies across the Atlantic in London.

HEIGHTENED SECURITY IN FERGUSON

On Tuesday night, tensions in Ferguson eased with less arsons and lootings than a day earlier after Missouri deployed about 2,000 National Guard troops -- reserve troops that state governors can call up during emergencies -- in and around the city.

"The ramped-up presence and action of the Missouri National Guard has been helpful," Missouri Governor Jay Nixon said Wednesday.

Still, police made 44 arrests as demonstrators set fire to a squad car and broke windows at City Hall. Protesters threw stones and bottles at the police, who dispersed the crowds using smoke shells and tear gas.

Volunteer clean-up crews, including children and families, swept the streets of Ferguson. Many residents hoped that the relative calm of the daylight hours would last through the night and into Thursday's Thanksgiving holiday.

Brown's parents made public calls for peace in the run-up to Monday's announcement and their representatives said Tuesday that the people setting fires were not on Brown's side.

COAST-TO-COAST PROTESTS CONTINUE

Ferguson, a northern suburb of St. Louis, has a population of 21,000 with more than 60 percent African-American.h Wilson, 28, told ABC News that he believed his conscience was clear and he had acted correctly.

In response, Brown's mother Lesley McSpadden said on NBC's "Today" show that Wilson's remarks added "insult after injury" and were "so disrespectful."

U.S. Attorney General Eric Holder said Monday that the Department of Justice will continue investigating Brown's death.

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.

Brown's death brought up issues in a country where tensions between police and black Americans have been strained for decades, with many blacks feeling the U.S. legal system and law enforcement authorities do not treat them fairly.

In Boston, more than 1,500 people participated in the protests Tuesday and 51 were arrested, including students from Harvard University, Tufts University and other local colleges.

In Los Angeles, protests lasted from Monday night to Tuesday afternoon. The Los Angeles Police Department declared Tuesday morning another citywide tactical alert in anticipation of more protests.

Some protesters blocked one of the freeways in the region Monday night and stopped the traffic for more than one hour.

Around 150 protesters marched through South Los Angeles to downtown Tuesday afternoon. Some of them ran into a skirmish line of police and some marchers jumped on top of police cruisers.

Protesters carried signs with slogans such as "Not Anti-Cop; Anti-Brutality" and "Arrest Darren Wilson."

Los Angeles police chief Charlie Beck told the media that while lawful protests will be respected, people who break the law or try to stop freeway traffic will be arrested.

In New York, ten people were arrested as thousands protested for a second night. The arrests occurred Tuesday night in Times Square, as four people were charged with resisting arrest and six with disorderly conduct, the New York Police Department said Wednesday.

However, police say there were no injuries and the protests were largely peaceful.

PROTESTS SPREAD TO LONDON

The public uproar is spreading across the Atlantic as thousands protested in London on Wednesday holding signs reading "Black lives matter" and chanted "Hands up, don't shoot," the slogan adopted by U.S. protesters.

At a rally outside the U.S. embassy, relatives of black men killed by police in Britain addressed the crowd.

"We need to send a message to Mike Brown's family," said Carol Duggan, the aunt of Mark Duggan, a 29-year-old black man whose shooting by police in 2011 was followed by riots.

"We feel the pain, we know the pain, of losing somebody at the hands of the police," she said. "That is why we stand in solidarity with the community of Ferguson. I feel they are very strong and brave people."

British anti-racist activists also urged people to protest against the decision at the U.S. Embassy at 0530 GMT on Wednesday.

"We condemn the decision of the grand jury not to indict Ferguson police officer Darren Wilson for killing 18-year-old Michael Brown in St. Louis. This comes on the same day that Tamir Rice, a 12-year-old boy, was shot dead by the police after carrying a toy gun," the Stand Up To Racism organization said in a statement.

The organization then called on people to join them at the U.S. Embassy for "an emergency peaceful protest," it added.

Diane Abbott, a member of the British Parliament and supporter of the protest, said the anger and disruption caused by the decision "extends beyond the killing of Brown right to the root of long-standing issues with the criminal justice system."