Twenty-six police officers have been shot and killed in the United States so far this year, an alarming increase from this point in time last year, according to a law enforcement watchdog group.

Data from the National Law Enforcement Officers Memorial Fund (NLEOMF), which tracks death of on-duty officers, show that 44 percent more officers have been killed by shootings in 2016 than at this point in time in 2015.

The deaths of five officers in Dallas, Texas, from sniper fire on Thursday raised the national total to 26. However, even before that attack, the figure was still higher than the number of police deaths at the same time last year.

Nick Breul, director of research for the NLEOMF in Washington, DC, said the Dallas attack was the latest of 11 ambushes of police officers so far this year across the US.

“That's certainly a concern for us. It's troubling and it's something that we watch,” Breul, a former police officer, told USA Today.

“It's really an assassination. You're taking advantage of an officer and you're ensuring that you're able to kill them through them either being vulnerable or through a complete surprise attack,” he added.

This is while nearly 500 people have been killed by police in the US during the first six months of 2016.

African Americans continued to be shot at 2.5 times the rate of whites. About half of those killed were white and about half were minorities, according to a survey by the Washington Post published on Thursday.

Tensions have once again escalated between law enforcement and communities of color over the deaths of two African-American men, Alton Sterling and Philando Castile, at the hands of police earlier this week.

Thousands of people took to the streets in cities across the US on Friday to denounce police violence against African Americans.

Protesters blocked traffic on major roads in New York City, Atlanta, and Philadelphia.

As many as 74 arrests were made in Rochester, New York, over disorderly conduct, police said.

Rallies were also held in Phoenix, where police deployed pepper spray to disperse a crowd in downtown. Three people were arrested for throwing rocks at officers.

In Baton Rouge, Louisiana, where Sterling was killed on Tuesday, police in riot gear faced off with several hundred protesters outside the city’s police department.

The demonstrations came a day after a sniper, identified as Army reservist Micah Xavier Johnson, targeted police in Dallas during a peaceful protest against police violence, allegedly citing revenge for recent police shootings as a motive.