Eleven police officers were shot, four of them fatally, when two snipers opened fire with rifles during a protest over police shootings in downtown Dallas Thursday evening, police said.
Police cornered one of the suspects in a garage and were negotiating with him, Dallas Police Chief David Brown said in a televised news conference.
He said authorities have reason to believe that the suspects had threatened to plant a bomb "in the downtown area."
Those who perpetrated the attack "planned to injure and kill as many law enforcement officers as they could," Brown said.
Authorities released a photo of a "person of interest" wearing camouflage and carrying a rifle.
"An intensive search for suspects is currently underway," Brown said in an earlier statement.
At least four of the officers belonged to the Dallas Area Rapid Transit agency, including one of those who died, according to the agency's Twitter account.
An agency spokesman said the officers did not appear to be together when they were shot.
A Police Department spokeswoman emailed a message to reporters asking them to "please be patient while we sort through all of this information as this is clearly still an active scene."
Video shot by a Facebook user appeared to show officers ducking for cover as shots rang out.
Hundreds of demonstrators had turned out earlier in the evening for a protest at Belo Gardens and a march to Main Street Gardens, according to the Dallas Morning News.
