Tunisian security forces have begun a manhunt for a third attacker in the assault on the Bardo museum that killed 21 people, mostly foreign tourists, the president has said.

Tunisia's Interior Ministry said on Sunday it was seeking the whereabouts of Maher bin Al-Moulidi Al-Qaidi, four days after two of the other gunmen involved in the attack were killed.

President Beji Caid Essebsi told French TV network iTele that the attack involved "three aggressors" and that the third man had escaped.

"Two were killed, but there is one who is now on the run," he said. "In any case, he will not get very far."

Maher bin Al-Moulidi Al-Qaidi has been named as a primary suspect.

Authorities had earlier released security camera footage showing two of the gunmen walking through the museum, carrying assault rifles and bags.

At one point they encountered a third man with a backpack walking down a flight of stairs. They briefly acknowledged each other before walking in opposite directions.

The footage was accompanied by two stills, said to be showing the bodies of the two gunmen - named as Yassine Laabidi, 20, and 26-year-old Hatem Khachnaoui. Both men were killed after the assault.

The two Tunisians reportedly trained in neighbouring Libya and left the country last December, Rafik Chelly, the country’s secretary of state, said days after the attack.

On Saturday, Essebsi said security "failures" had helped facilitate the attack on the museum, the deadliest on the north African country since the 2002 suicide bombing in Djerb.

"There were failures" which meant that "the police and intelligence were not systematic enough to ensure the safety of the museum", Essebsi told the weekly Paris Match .

Essebsi also said there were as many as 10,000 young Tunisian "jihadists" in all.

"Among the often desperate young unemployed, the call to jihadism has worked," he said.

"Four thousand Tunisians have joined jihad, in Syria, Libya and elsewhere, and some 500 have already come back here, where they pose a threat. That is not to mention the five or six thousand others we have succeeded in preventing from leaving."

Twenty-one people, all but one of them foreign tourists, were killed when the gunmen stormed the museum last Wednesday, in an attack claimed by the Islamic State of Iraq and the Levant (ISIL) although authorities said they had not established any link with armed groups.

Essebsi, however, stressed that the country's security forces "responded very effectively to quickly put an end to the attack on the Bardo, certainly preventing dozens more deaths if the terrorists had been able to set off their suicide belts", he was quoted as saying on the Paris Match website.

Guards on coffee break 

A senior Tunisian politician on Friday said the guards supposed to be protecting the museum and the nearby Parliament were having coffee at the time of the assault.

"I found out there were only four policemen on security duty around the Parliament [compound], two of whom were at the cafe. The third was having a snack and the fourth hadn't turned up," deputy speaker Abdelfattah Mourou told the AFP news agency.

Authorities on Saturday launched a crackdown, arresting more than 20 suspects in a nationwide security operation.

Ten of those arrested are believed to be directly involved in the Bardo attack, Interior Ministry spokesman Mohamed Ali Aroui said.  

"There is a large-scale campaign against the extremists," he said. The ministry released a photograph of another suspect and asked Tunisians to help with information.  

The government plans to deploy the army to major cities to improve security following the shootings, officials said.

Source: Agencies