At least 18 tourists are now believed to have been killed following an attack on the Bardo Museum in Tunis, capital of Tunisia.
Both gunmen were also killed in the incident, along with three Tunisians, with a policeman among them.
One of the gunman, Yassine Laabidi, was known to police authorities have confirmed, but there were no “specific” links to known militant groups.
Two or three accomplices of the gunmen are still at large, with a search presently underway to capture them.
The second gunman, both of whom are believed to be Tunisian, has been named as Hatem Khachnaoui.
The tourists killed in the attack include visitors from Japan, Italy, Colombia, Australia, France, Poland and Spain, officials said. More than 40 people were also injured.
On Thursday, three people - two Spanish tourists and one Tunisian museum worker - were found at the museum after having hidden there overnight.
Islamist militants In Tunisia have tried to derail the democratic transition.
The county is one of the few which continues along the path following the Arab Spring.
Tourism is a key sector of Tunisia’s economy, however concerns about security in the country have increased in recent months as neighbouring Libya has become increasingly unstable.
The UNWTO condemned the attack.
A statement read from secretary general Taleb Rifai: “UNWTO conveys its heartfelt sympathy to the families of the victims who lost their lives or were injured, and expresses its solidarity to the people and the Government of Tunisia and to the governments of all nationals who were killed.
“This act of violence deserves the condemnation of the international community. As part of the global tourism family, we are shocked by these horrible attacks.
“The relatives and friends of the victims are in our thoughts and we once more convey our solidarity with the people and the Government of Tunisia.
“Tourism is a lifeline for the economy of Tunisia and we will continue our support to ensure that tourism continues to provide development opportunities to its people,” he added.