Tunisia's prime minister says that the slow response of police to last week's deadly attack on a tourist resort was a major problem.
Habib Essid took part in a minute's silence to remember the 38 people who were killed in the town of Sousse, south of Tunis, a week ago.
He said he was deeply sorry for the attack, in which 30 Britons died.
Mr Essid said the government believed there was only one gunman, and that he had links to a known terrorist group.
Islamic State (IS) claimed responsibility for the attack.
Reports in the British press said the assault took place over almost 35 minutes, and that the gunman was able to return to kill some of the wounded before the police arrived.
He was eventually shot dead in an alley.
"The time of the reaction - this is the problem," Mr Essid told the BBC's Richard Galpin. Police had been "blocked everywhere", he added.
Mr Essid said Tunisia sent its condolences to the British government and to the Queen over the deaths of the British tourists.
"We feel really sorry about what happened," he said. "They were our guests. They came to spend their vacation with us, but what happened is a horror, unacceptable."
The gunman, identified as Seifeddine Rezgui, came onto the beach from the sea either by jet ski or speedboat at about midday.
He started shooting on the beach, entered the Hotel Imperial Marhaba and ran out of the front of the hotel before the police shot him dead.
The attacker had travelled to Libya between December 2014 and January 2015, Mr Essid said.
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.
The group that planned this attack was also behind the deadly shootings in the Bardo Museum in Tunis in March, Mr Essid added.
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.
It was the deadliest attack in Tunisia's recent history.