Kenya's interior minister said Wednesday that only an "insignificant" number of bodies were thought to remain in the wreckage of Nairobi's Westgate mall.

Countries including Britain, the United States, Israel, Germany and Canada are assisting the probe into the four-day siege by Islamist gunmen, which left 67 dead and dozens more missing, Joseph Ole Lenku told reporters.

The Somalia-based militants who stormed a Kenyan mall had a detailed plan and had hidden weapons at the scene beforehand, according to U.S. officials cited by the New York Times Wednesday.

According to the report, a hand-picked group of English-speaking fighters from the Shebab, an Islamist rebel group, had trained for the assault in Somalia for weeks beforehand.

Impoverished Somali refugee camps in northern Kenya could not be more different from upmarket malls in the capital Nairobi, but attacks by Somalia's Shebab insurgents have affected them both.

Now, as Kenya reels from a four-day siege by the al-Qaida-linked gunmen in Westgate mall, Somalis in the country are terrified of retaliatory attacks.

A Frenchman caught up in the Nairobi mall attack who survived by hiding for five hours in his bank said Wednesday he had an overpowering desire to kill the militants when he saw a child's corpse.

The man, who identified himself only by his first name, Eric, said that his initial feelings of helplessness turned to rage when he saw the body and thought it could have been his daughter.

A British national has been arrested in Nairobi following the bloody attack on a shopping mall by armed Islamists, a spokeswoman for the Foreign Office said on Wednesday.

"We can confirm the detention of a British national in Nairobi and we are making contact to offer standard consular assistance," she told AFP.

Kenyan troops and rescue workers scoured the wreckage of a Nairobi shopping mall Wednesday for bodies and booby-trapped explosives after a four-day siege by Islamist gunmen left 67 dead and dozens more missing.

Rescuers wore face masks and some soldiers wrapped scarves around their mouths because of an overpowering stench inside the Westgate center, once the capital's most upmarket mall. A large part of the complex has collapsed after heavy explosions and a fierce fire.

The International Criminal Court on Tuesday denied a request to postpone Kenyan President Uhuru Kenyatta's trial for crimes against humanity.

The Hague-based court rejected Kenyatta's request for the November 12 trial date to be pushed back, saying the defense had already had enough time to prepare their case, an official document said.

Somali Prime Minister Abdi Farah Shirdon said Tuesday that those behind Nairobi's deadly mall siege which has been claimed by Somalia's Shebab militants, must be brought to justice.

"Those responsible must be held accountable," the premier said during a U.N. human rights meeting in Geneva. "This tragedy has brought our countries closer."

Israel, which is said to have aided Kenya during the deadly attack on a Nairobi mall, has long viewed East Africa as a region of major strategic and economic importance.

"Kenya, Ethiopia and Eritrea are three countries which are crucial for Israel because they act as a buffer zone in a region which is seeing Islamic fundamentalism growing at a rapid pace," said Galia Sabar, head of African studies at Tel Aviv University.

Kenya's president announced Tuesday that a siege of a Nairobi shopping mall was over, but said losses from the attack by Islamist gunmen were "immense" and at least 67 people had died.

"We have ashamed and defeated our attackers, that part of our task is completed," President Uhuru Kenyatta said in a televised address to the nation.