Shots were fired from an armored van in an attack on Dallas Police headquarters early on Saturday, police said, and an explosive device was later found outside the building.
Dallas Police Chief David Brown told reporters that witnesses said as many as four suspects were involved in the incident, which began around 12:30 a.m. He said that a motive was not yet known.
Brown said when police responded to reports of automatic gunfire, the van rammed a squad car and at least one person opened fire. The van drove off when the police returned fire and the police gave chase, Brown said.
The van stopped in a fast food restaurant parking lot in the city of Hutchins, some 10 miles (16 km) south of Dallas, where there was another exchange of gunfire.
Brown said police negotiators had since been in contact with one of the suspects inside the van, who identified himself as James Boulware.
Brown said that the suspect had said that police had taken his son and had accused him of being a terrorist. Brown said that the man then threatened to "blow us up."
Four bags were found scattered around police headquarters, one of which had explosives inside, Brown said. Nearby residents were being evacuated from the area, he said.
No officers have been injured, but the suspect speaking with police said he had been hurt, Brown said.
A video of the incident on social media showed a police officer approaching a black van with a flashlight as two other police cruisers pulled up behind the vehicle. The officer then abruptly turned and ran away and then a volley of gunshots could be heard.
In another video, the van could be seen ramming a police cruiser before gunfire rang out and the vehicle drove off.