Grand-Bassam (Ivory Coast) (AFP) - Ivory Coast President Alassane Ouattara vowed Monday that the country would not be "intimidated by terrorists", as the death toll in the country's first jihadist attack climbed to 18.

Armed with grenades and assault rifles, gunmen on Sunday stormed three hotels and sprayed the beach with bullets in the resort of Grand-Bassam, a sleepy town popular with expats just a short 40 kilometre drive from the commercial capital Abidjan.

The attack claimed by Al-Qaeda in the Islamic Maghreb (AQIM) left 15 civilians dead, including a German woman, as well as killing three special forces troops, the government said. A total of 33 people were injured, 26 of whom are still in hospital.

France said four of its nationals were among the dead.

AQIM's real target was France, analysts said, punished both as Ivory Coast's former colonial master and for hunting down jihadists in Mali and elsewhere.

"The Ivory Coast will not allow itself to be intimidated by terrorists", Ouattara said in a statement broadcast on radio and television.

"Ivory Coast is standing up, standing up to fight the cowards and protect its people."

He vowed to work with countries in the sub-region, on the continent and with our "other international partners to reinforce our cooperation to fight these terrorists".

Interior Minister Hamed Bakayoko said "three terrorists were killed" in the assault.

Asked whether more gunmen were involved -- some witnesses had reported several attackers -- the minister said "we're still looking. We don't suspect more but we're making sure we carry out the widest possible sweep."

Along with a three-day national mourning period starting Monday, he said the West African nation would boost security at "strategic sites and in public places... (such as) schools, embassies, international institutions... and the borders."

In the latest such jihadist assault in West Africa, witnesses described the panic as gunfire rang out across the sand and an assailant shouted "Allahu Akbar" -- Arabic for "God is greatest".

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- 'I thought this was it' -

Condemnation came from around the world with UN Secretary General Ban Ki-moon pledging to help government "efforts to bring the perpetrators of these crimes to justice."

French President Francois Hollande's office said his country will support Ivory Coast "to fight terrorism and considers that cooperation between all the states threatened by terrorist groups, particularly in West Africa, must intensify more than ever".

It was the third such attack in four months in West Africa and a blow to a nation working to lure back foreign tourists to its palm-fringed beaches and rainforests as it recovers from a brutal civil war.

The German victim was named as 51-year-old Henrike Grohs, who headed Abidjan's Goethe Institute, the German language centre's secretary-general said.

Grand-Bassam is packed at weekends with visitors drawn by its magnificent beaches and UNESCO-listed colonial-era buildings.

Carine Boa, a Belgian-Ivorian teacher at an international high school in Abidjan, was at one of the beach bars with her two sons when the gunmen arrived.

"We were really scared. We thought of the people at the Bataclan," she said, referring to the concert venue attacked by gunmen during November's terror attacks in Paris that left 130 people dead.

"I thought this was it for us," she said.

Some witnesses reported seeing more than three assailants, contradicting the official version.

"When they arrived, it was a woman who brought their luggage to put it in the bungalow," said one witness.

"They changed (their clothes), there were seven. The first person who came out was wearing a white top, and then he had a scarf on his head. He faced a child and then said 'Allahu Akbar' and fired at the child. When we saw that we ran."

- Fears run high -

The US-based SITE Intelligence Group said AQIM, the terror group's North African affiliate, had claimed responsibility.

West African nations have scrambled to boost security after jihadist attacks in November and January on upscale hotels in the capitals of Mali and Burkina Faso that were also claimed by the group.

Sunday's attack also bore grim similarities to the Islamist gun and grenade assault on a Tunisian beach resort last June, which left 38 foreign holidaymakers dead.

"Hitting Ivory Coast is clearly a way of attacking France's historical ally in the region," said Antoine Glaser, author of a recently published critical account of French colonisation in Africa called "Arrogant comme un Francais en Afrique" (Arrogant like a Frenchman in Africa).

Robert Besseling of Exx Africa, a specialist intelligence company, said the attack should not have come as a surprise.

"Cote d'Ivoire has been receiving warnings for at least a year from France's intelligence service that Islamist militants are planning to attack major cities," said Besseling, using the French name for Ivory Coast.