NAIROBI (AFP) - Kenyan police are holding five people over last month's attack on Nairobi's Westgate mall, a top officer said on Tuesday, adding they hoped to charge them soon.

At least 67 people were killed in the attack on the upmarket mall claimed by Somalia's Al-Qaeda-linked Shebab insurgents.

Mr Ndegwa Muhoro, head of Kenya's Police Criminal Investigation Department, told reporters that investigations were still ongoing into exchanges of mobile telephone text messages in the days prior to the four-day siege that began on Sept 21.

"We wanted to arraign five of the terrorists in court yesterday, but we have decided to first investigate an SMS exchange of the terrorists which occurred on September 17," he said.

"There are various issues which need thorough investigation, we cannot rush to court." However, all gunmen - totalling just four, not the dozen that security forces had initially reported - are understood to have died during the attack.

"Interpol is also assisting us in the investigations, including the analysis of four bodies suspected to be of the terrorists," Mr Muhoro said.

A telephone call was made during the attack to Norway, he added.

A Norwegian citizen of Somali origin is suspected of being one of the attackers, a 23-year-old named by media as Hassan Abdi Dhuhulow.

Witnesses in the mall described how the fighters stormed the crowded complex firing from the hip and hurling grenades at shoppers and staff. The gunmen coldly executed scores of people, with witnesses recounting how in some cases they called out to those wounded, then finished them off at close range.