(Reuters) - Morocco was counting the cost to its vital tourism industry on Friday from an explosion at a busy Marrakesh cafe that killed 15 people in an attack described by the government as a terrorist act.

Moroccan officials have not said who was responsible for the Thursday blast. Western security analysts said it was likely to have been carried out by Islamist militants trying to damage the tourism industry on which the country depends.

The Interior Ministry said seven of the 15 dead had been identified and included two French citizens, two Canadians, a Dutch national and two Moroccans.

Israel's foreign ministry said two of the victims, a man and a woman, were Jews living in Shanghai and that the woman apparently had Israeli citizenship.

Standing outside the wrecked cafe in Jamaa el-Fnaa square, Morocco's best-known tourist spot, German tourist Julia Zashou and her mother sobbed as they looked at the site. They said they used to visit the venue frequently.

"We don't understand. Marrakesh is such a nice place," said Zashou. "What happened is a catastrophe for tourists."

The attack, in which 23 people were also wounded, is the deadliest Morocco has seen since suicide bombers killed 33 people in coordinated strikes on Casablanca eight years ago. There was no immediate claim of responsibility.

"Preliminary investigation ... suggests that this was a terrorist act caused by an explosive device," the official MAP news agency quoted Interior Minister Taieb Cherkaoui as saying.

He was later reported to have said the bomb was detonated remotely.

"Those who usually resort to this method... are known which leads us to believe that the risk remains present and that we have to stay on watch and be on guard," he said.

Quoting an unnamed security official familiar with the investigation, the Lakome.com news portal said the device was detonated by a suicide bomber who was freed from prison two months ago where he was serving a sentence for rape.

HAVEN OF STABILITY

The attack adds to the challenges facing Morocco's ruler, King Mohammed, at a time when he is trying to prevent uprisings elsewhere in the Arab world from reaching the kingdom, which is usually seen as a haven of stability in a volatile region.

The monarch has promised to reform the constitution to placate protesters. But more protests are planned for Sunday to demand a change of government and more democratic freedoms.

Tourism is Morocco's biggest source of foreign currency and the second biggest employer after agriculture.

Tourism Minister Yassir Znagui on Friday visited Marrakesh's Ibn Tofail hospital, where many of the victims -- including several seriously wounded foreigners -- were being treated.

"It's difficult to talk about the consequences ... For the moment, the priority is to be near the victims and their relatives," he said.

At Marrakesh's airport, where an official said security had been stepped up, there was no evidence that holidaymakers were cutting short their vacations. But many said they would reconsider visiting the country in the future.

"We used to come to Marrakesh on an annual basis but next year we will go somewhere else," said French tourist Jean-Pierre Arnault. "Attacks happen all over the world, but this one targeted tourists. It's serious."

A German pensioner who gave only her family name, Hilgers, said at the airport: "I have not brought forward my departure but some tourists in the hotel where I stayed did."

"We have always thought that Morocco is a peaceful country, the people are very nice. I think what happened deals a very serious blow to tourism. It disturbs people."

NAIL BOMB

Hicham Nejmi, a doctor at the Ibn Tofail hospital, said medics had found nails in most bodies, evidence the bomb-makers had packed the device with shrapnel to cause maximum harm.

Moments after Thursday's explosion, a Reuters photographer said he saw rescue workers pulling dismembered bodies from the wreckage of the cafe.

Western security analysts said the bombing carried the hallmarks of Islamist militants, possibly liked to al Qaeda's north African wing, al Qaeda in the Islamic Maghreb (AQIM).

Last week, men claiming to be Moroccan members of AQIM appeared in a video posted on YouTube threatening to attack Moroccan interests.

The ESISC think tank said: "We assess it must be the work of a well organized terrorist organization."

An opposition group urged the authorities against using the attack as an excuse to crack down on rallies planned for Sunday. The banned Justice and Charity Islamist group called the bombing a "cowardly and criminal act."

"The objective of the attack is to spread fear and to disrupt the popular protest in Morocco," the group said.

(Additional reporting by Souhail Karam in Rabat, Tracy Rucinski in Madrid and Ari Rabinovitch in Jerusalem; Writing by Christian Lowe; Editing by Maria Golovnina)