Tunisian police were slow to intervene in the gun attack that killed 38 mostly British tourists at the beach resort of Sousse, prime minister Habib Essid told the BBC on Friday.
"The time of the reaction - this is the problem," Essid told the BBC. Police had been "blocked everywhere," he added.
"We feel really sorry... what happened is a horror, unacceptable," he said.
A one-minute silence was held simultaneously in Sousse and across the UK to commemorate the victims of last Friday's attack. Essid attended the Sousse ceremony held on the beach.
The assault on a hotel beach reportedly took place over almost 35 minutes and the gunman was able to return to kill some of the wounded before police arrived.
Identified as Tunisian student Seifeddine Rezgui, he was eventually shot dead by police in an alley in Sousse, some reports said as he was praying.
Police are holding eight suspects in custody on suspicion of being directly linked to the attack, which jihadist group Islamic State has claimed. Four others who were held have been released.
They have also deployed 1,377 armed security agents at hotels and on beaches to protect people.
As well as the 30 Britons, other victims of the Sousse attack included three Irish citizens, two Germans, one Belgian, one Portuguese and one Russian national.
In March, IS killed 21 foreign tourists and a Tunisian policeman at the famous Bardo museum in Tunisia's capital, Tunis.
