Authorities, protest leaders and the mother of one of the victims have appealed for calm as over 300 demonstrators, angry at the latest killings of black men by police officers, were arrested in a weekend of intense, sometimes violent nationwide protests.

Late Sunday and into Monday morning, almost fifty protesters were bundled into the back of police vans in Baton Rouge, Louisiana, while a handful in Atlanta, Georgia were also arrested.

The mayor of Memphis, TN, another city where demonstrators took to the streets over the weekend, said he remained “hopeful” that his city’s peaceful protests Sunday would signal a willingness of Black Lives Matter activists and police to hold a “respectful” dialog.

“We are here to fully support those conversations — and my door has always been open,” Mayor Jim Strickland said Sunday night in a statement.

“But we want to do it in a legal way, as well. Let me be clear: you can exercise your First Amendment rights without breaking the law.”

Valerie Castile, mother of Philando Castile, one of two African American men killed by police last week in separate shootings, sent a statement to media via her attorney Sunday.

“We urge all people to remain peaceful in all demonstrations throughout our community and our nation,” the statement read.

“When demonstrations become violent, it disrespects my son and his memory. Philando was a man of peace and dignity.

“I ask you to at all times remain peaceful in your expressions of concern regarding his death at the hands of the police. I promise that we will not rest until justice prevails.”

In Boston, organizers for Sunday’s demonstration announced on Facebook: “This is a peaceful protest. Please keep violence at home.”

Despite the calls for calm from all sides, at least 312 people have been arrested over the weekend at protests from New York to Chicago, and in St. Paul, Minnesota, and Baton Rouge, Louisiana, where two black men, Philando Castile and Alton Sterling, were shot to death by police.

The two men’s deaths in turn spurred a lone shooter in Dallas to kill five police officers during a Black Lives Matter protest.

Prominent activist arrested

Black Lives Matter activist DeRay Mckesson, a public school administrator who is considered among the movement’s loudest voices, was among 125 people arrested Saturday night in Baton Rouge, where Alton Sterling was shot and killed last week.

The activist was walking along a major roadway and live-streamed his arrest for obstruction on Saturday on Periscope. Another 124 protesters were arrested.

In St. Paul, about 102 protesters were arrested. They were demonstrating against the killing of Philando Castile, a school nutrition services supervisor. Last week, Castile was driving a car and was with his girlfriend, Diamond Reynolds, when they were pulled over for a broken taillight.

Reynolds posted a Facebook video of the aftermath of Castile’s shooting. Castile told the officer he was armed and had a concealed carry permit, she said. The officer asked him for his license and registration and as he went to retrieve those items, the officer shot him multiple times, she explains as the recording continues.

Baton Rouge Police Chief Carl Dabadie Jr., at a press conference Sunday to explain the arrests, acknowledged a Baton Rouge officer pointed an assault weapon at protesters, but he said a supervisor immediately intervened to secure the weapon from her.

“That is being addressed by us also,” Dabadie said. “My officers are human. They are tired. They are scared.”

Louisiana Gov. John Bel Edwards, who called the press conference, said most protests had been peaceful — with most arrests for minor offenses — and blamed outside agitators for incitements to violence.

“That will not be tolerated — we don’t operate like that in Louisiana,” Edwards said. “The best way to honor the memory of Alton Sterling, the Dallas officers and Philando Castile, is through peaceful protest.

“It is critically important that you follow the directions of law enforcement.”

Sunday protests

More marches took place around the nation Sunday.

In Washington, on the fourth night of protests, several hundred protesters who had marched two miles to Union Station accepted without complaint the news from organizers and police that they could not march on the Capitol without a permit.

At the rally, the Rev. Matthew Watley, of Reid Temple AME Church, said people are looking for healing after having old wounds of racism reopened by the events last week.

He also said he wants the community to work with law enforcement.

“We don’t want to be profiled as African-Americans, we also can’t profile law enforcement because the supermajority of them are trying to do the right thing,” he said.

Dallas cop-killer had ‘other plans’

The same week Sterling and Castile were killed, a gunman killed five police officers at a Black Lives Matter rally in Dallas.

Their killer was an Afghanistan war veteran, 25-year-old Micah Xavier Johnson from the Dallas suburb of Mesquite, Texas.

Johnson was plotting larger attacks, Dallas Police Chief David Brown said in an interview with CNN’s Jake Tapper on “State of the Union” Sunday.

He said police found bomb-making materials and a journal at the shooter’s home that suggested he’d been practicing detonations and appeared ready to take aim at larger targets.

Black Lives Matter protesters condemned the Dallas killings, calling the attack on law enforcement a tragedy not just for those affected but also for the nation.

“Black activists have raised the call for an end to violence, not an escalation of it. (Thursday’s) attack was the result of the actions of a lone gunman,” the group said.

“To assign the actions of one person to an entire movement is dangerous and irresponsible. We continue our efforts to bring about a better world for all of us.”

Three other shootings, in Tennessee, Missouri and Georgia, have endangered police during rallies.

Black Lives Matter crosses the Atlantic

Hundreds of demonstrators took to the street in London Sunday to show support for the Black Lives Matter movement. Kicking off from Oxford Circus, London, where crowds marched toward the U.S. Embassy chanting “No justice, no peace” and “Hands up. Don’t shoot!” Some roads were brought to a standstill.

London resident Aifur Rahman, who described himself on social media as a mathematics graduate, said the event was astonishing in its protest against police shootings in the United States.

“It brought many communities together and gave everyone a sense of unity in the fight against oppression and racial inequality,” he said.

One man in attendance, named Banditsu, told CNN: “Black lives matter, I’m tired of seeing my brothers and sisters becoming a hashtag. Every day I wake up another black person is dead, that’s why I’m here today. “