U.S. President Barack Obama will cut short his trip to Europe to return to Dallas, Texas, where five police officers were slain by a lone gunman who said he wanted to "kill white people."
Obama still plans to travel to Spain on July 9 after attending the NATO summit in Warsaw, but he will scale back his planned activities there with the goal of arriving in Dallas early next week, the White House said on July 8.
Obama had earlier denounced as "despicable" the killings by U.S. Army reservist Micah Johnson, who had served in Afghanistan and amassed an arsenal of guns, ammunition, and bomb-making materials in his home before being killed by police.
Top U.S. officials said on July 8 that they believe that Johnson, who had told police during negotiations that he was acting alone and targeting white people because he was upset about police shootings of black people, was indeed a lone gunman.
While police initially rounded up several suspects, "there appears to have been one gunman" in the attack that killed five and wounded nine others during a July 7 street protest, said Homeland Security Secretary Jeh Johnson, adding that the shooter had no known "links to or inspiration from any international terrorist organization."
In an apparent copy-cat crime on July 8, a man shooting indiscriminately at cars on a Tennessee highway killed one woman and injured three other people. He told police he was angry about police violence against African-Americans.
Police officers also were ambushed and wounded in Missouri and Georgia on July 8.
While the Dallas shooter Johnson did not take inspiration from overseas militant groups, on his Facebook page he had endorsed several U.S. militant black groups, including the Black Panthers, the Nation of Islam, and a black nationalist poet who after this week's police shootings of blacks had called for violent retaliation by African-Americans.
"The suspect said he was upset at white people. The suspect stated that he wanted to kill white people, especially white officers," Dallas Police Chief David Brown said.
Johnson's deadly attack fueled mounting tensions across the United States over race, gun control, and police violence -- all issues raised by earlier mass shootings and police shootings, and hotly debated in this year's acrimonious presidential campaign.
Johnson, who police killed using explosives after an attempt at negotiations, was reacting to incidents earlier in the week in Minnesota and in Louisiana in which white police officers shot and killed black men as they were confronting or arresting the men.
Those incidents resembled widely publicized police shootings of unarmed black men in 2014 and 2015 and sparked angry but peaceful protests in cities around the country besides Dallas on July 7.
The protests continued on the evening of July 8, with thousands gathered in Los Angeles, Atlanta, Boston, and other cities to denounce not only the police shootings of blacks but the killing of the Dallas police officers.
Hundreds of people also demonstrated in London, England to show solidarity with the U.S. Black Lives Matter movement.
Philadelphia and some other cities are planning a "Weekend of Rage" to draw attention to disparate police treatment of blacks and whites.
Obama, who has spoken out repeatedly and often emotionally about mass shootings and incidents involving black men being fatally shot by white police, pledged to bring those responsible to justice for the attacks on police.
"There has been a vicious, calculated and despicable attack on law enforcement," Obama said in Warsaw, where he arrived July 8 for a NATO summit.
"We will learn more undoubtedly about their twisted motivations. Let's be clear. There is no possible justification for these kinds of attacks or any violence against law enforcement," Obama said.
In a July 8 statement, he ordered the flags on all U.S. government buildings to be flown at half-staff until July 12 "as a mark of respect for the victims."
White House officials had been in contact with officials in Dallas on July 8 to offer their support, White House spokesman Josh Earnest said, adding that Obama is concerned about the ease with which guns can be obtained in the United States.
"The president's views about the impact that the easy availability of guns has on our community is a significant source of concern for him," Earnest said.
Hillary Clinton and Donald Trump, the presumptive Democratic and Republican presidential candidates, respectively, both canceled political events scheduled for July 8 out of respect for the police officers killed in the attack.
Trump, who has received the backing of the country’s top gun rights organization, called the slaying of the officers "a coordinated, premeditated assault on the men and women who keep us safe." Clinton, who has called for stricter gun-control laws, said she is mourning the officers killed "while doing their sacred duty to protect peaceful protesters."
Seven other police officers and two civilians were injured in the shooting attack during the rally to protest killings of black men by white police officers.
U.S. Attorney General Loretta Lynch, meanwhile, said that the Justice Department is doing all it can to assist Texas officials investigating the attack.
Speaking at a July 8 news conference, she urged Americans not to let the racially charged shootings over the past week become the "new normal" and called for "calm, peaceful" action to address division in society.
The hundreds of demonstrators who were marching through Dallas July 7 were protesting against the shooting deaths of Philando Castile, who was killed by police near St. Paul, Minnesota, on July 6, and Alton Sterling, who was killed July 5 during an altercation in Baton Rouge, Louisiana.
In both cases, the officers were white; both Castile and Sterling were black. In both cases, cellphone video taken by bystanders of the incidents was shared widely, further fueling outrage.
In St. Paul, Minnesota, where Castile was shot, around 1,000 people gathered outside the governor's mansion, chanting "Hey hey, ho ho, those killer cops have got to go," and other slogans.
During a brief appearance, Minnesota’s governor said he believed the Castile killing could have been an instance of racism and that a state investigation was already under way.
In Minnesota, the labor union that represents the officer who shot Castile urged people to reserve judgment.
"We know that people are angry, discouraged and heartbroken," said Sean Gormley, executive director of Law Enforcement Labor Services. "We support an open, thorough, and objective investigation that we believe, in time, will provide the answers to the questions we all have."