National Guard spokesman Houcem Eddine Jebali said a patrol of two National Guard officers was attacked with a knife in the center of Sousse on Sunday.
"One died as a martyr and the other was wounded and is hospitalized," he said, adding "This was a terrorist attack".
The assailants took the officers’ gun and vehicle, but security forces followed them through the city's tourist area of El-Kantaoui, said Jebali. He said that in a firefight three terrorists were killed.
The attack on security forces came just two days after the government of Prime Minister Hichem Mechichi took power in the North African country.
Tunisia has been hit by a spate of militant attacks claimed by the Daesh and al-Qaeda terrorist groups since 2011, killing dozens of security personnel and foreign tourists.
An attack against security forces protecting the US Embassy in Tunis killed a Tunisian police officer and left several others wounded in March.
2015 was a particularly bloody year, with three major deadly attacks claimed by the Daesh group.
An attack at the capital's Bardo museum in March killed 21 foreign tourists and a security guard.
Just three months later, 38 foreign tourists were killed in the shooting rampage at Sousse. And that November, a bomb blast on a bus in central Tunis killed 12 presidential guards.