A sheriff's deputy was shot and killed on 28 August while filling up his car with petrol, in an "ambush" at a Houston petrol station, authorities said. A search was under way for the officer's killer, who was described as a male dressed in a white T-shirt, driving a red truck, the Harris County Sheriff's office said.

Deputy Darren H Goforth was in uniform and filling up his car with petrol when the gunman approached from behind and fired several shots, sheriff's office spokesman Deputy Thomas Gilliland told reporters.

"The deputy then fell to the ground. The suspect then continued over to him and shot the deputy again multiple times as the deputy laid on the ground," he said. Gilliland added there was "No apparent reason at all."

Live video from the scene in north-west Houston, about 20 miles from downtown, showed police tape across the perimeter of the petrol station. Dozens of officers were on the scene.

"We are actively searching for this suspect as right now. I can tell you that with diligence and justice this suspect will be caught and he will be brought to justice," said Gilliland.

Goforth was 47 years old. He had spent 10 years in law enforcement, and was assigned to the west district, police said.