TUNIS (AFP) - The guards supposed to be protecting Tunisia's parliament and the nearby national museum were having coffee at the time of this week's deadly assault, a senior politician said on Friday.

On Wednesday as gunmen mowed down foreign tourists, "there were no police around parliament and the museum," deputy speaker Abdelfattah Mourou told AFP.

"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," he said.

"It's a big failure," said Mourou, who pointed out parliamentarians had discussed the issue of security with police and the army on Tuesday, only to be told they lacked equipment.

The interior ministry was not immediately available for a reaction, although President Beji Caid Essebsi has said the speedy response of the security forces had "prevented a catastrophe".

The attack, claimed by the Islamic State jihadist group, killed 20 tourists and a policeman before the gunmen were killed by security forces.