A double suicide attack shook the Tunisian capital on Friday as assailants wounded six people including police guarding the US embassy, authorities said.

An explosion rocked the Berges du Lac district where the embassy is located around midday, causing panic among pedestrians and motorists in the area.

Two assailants died in the attack, the first to hit the capital since June 2019, according to officials.

Police said one attacker tried to enter the diplomatic mission but was prevented by police guarding it.

A policeman who witnessed the attack said a suicide bomber who was travelling on a motorcycle was also killed.

Body parts were seen strewn on the ground.

"The operation led to the death of two assailants, wounded five police and lightly injured a civilian," the interior ministry said in a statement without giving further details.

Police dispatched reinforcements to the area, including forensic experts as a helicopter flew overhead.

"It's tough to have to go on working when your colleagues have been wounded," a police officer at the scene of the attack said.

The US embassy said in a statement posted on Twitter: "Emergency personnel are responding to an explosion that occurred near the U.S. Embassy in Tunis.

"Please avoid the area and monitor local media for updates."

Tunisia faced a rise in jihadist activity after its 2011 revolution, with attacks killing dozens of security personnel, civilians and foreign tourists.

While the security situation has significantly improved since a series of deadly attacks in 2015, Tunisia has maintained a state of emergency for four years and assaults against security forces have persisted.

Before Friday the last attacks were in June 2019, when twin bombings targeted a police station on the outskirts of Tunis and a police vehicle on the capital's main throughfare.

A civilian and a policeman were killed in those attacks, while seven were wounded.

An attack at the capital's Bardo museum in March 2015 killed 21 foreign tourists and a security guard. 

In June the same year, 38 foreign tourists were killed in a shooting rampage at the coastal resort of Sousse.