Two suicide attackers on a motorcycle blew themselves up outside the US embassy in Tunis on Friday, wounding five police officers, the interior ministry said.
US Embassy officials confirmed the attack on Twitter, and urged people to avoid the area.
Security units were placed on a state of maximum alert, the interior ministry said. Hundreds of police swarmed around the scene and sharpshooters were visible on the roofs of nearby buildings.
The United States was outraged by the attack, a spokesman for the State Department said, and was saddened to hear reports of a fatality from Tunisia's security services.
"We are working with local authorities to investigate," he said.
Among the injured was a locally hired employee of the US Embassy, the spokesman added.
Witnesses saw a scorched, damaged motorbike and a damaged police vehicle a few metres from the embassy's main gate, as a helicopter whirled overhead. Sirens could be heard on the major highway linking the Berges du Lac district, where the embassy is located, with Tunis and suburbs in the north.
The interior ministry said the attackers both died. A civilian was slightly injured.
A police official said the suicide bombers tried and failed to enter the embassy compound. "The operation was doomed to fail," he said.
Politician Yosri Dali, head of the armed forces and security commission, said in an interview with Radio Mosaique that the attackers blew themselves up when a police patrol stopped them to ask where they were going.
There was no immediate claim of responsibility for the attack. Radio Mosaique identified the attackers as Zenidi Mohamed Selim, born in 1991 in Marsa and a resident of Kram; and Laaka Khoubaieb, born in 1993 in Marsa and a resident of Sidi Daoued.
Last summer, ISIS admitted to three blasts in the capital, including one near the French embassy that killed a policeman and another that wounded five people during a security operation to detain a suspect.
In July 2018, at least six police officers were killed in an Al Qaeda attack while on patrol in the Ain Sultan area of Jendouba province bordering Algeria.
Tunisia's critical tourism sector is highly vulnerable to militant violence and was devastated after two attacks in 2015 which killed scores of visitors at a beach resort and a museum.
Diplomats who have worked with Tunisia on its security capacity say it has grown more effective in preventing and responding to militant attacks in recent years.
An Al Qaeda group has been sheltering for years in the desolate, hilly terrain along a stretch of the border with Algeria and sometimes clashes with security forces there, but is regarded as having been closely contained.
Hundreds of Tunisians have also travelled to Iraq, Syria or Libya in recent years to join ISIS, and in 2016 members of the group rampaged across the border with Libya and fought the army in a border town, but were repulsed.
"The attack indicates that the security challenge remains a major challenge in Tunisia," local security analyst Ali Zarmedini said.