Kenyan forces in Somalia were warned of an impending Al-Shabaab attack 45 days before the group overran one of their bases, a Somali general says.
Kenya was given "clear and reliable intelligence" about the threat, General Abas Ibrahim Gurey told the BBC.
The Islamist militants say they killed more than 100 Kenyan troops in the attack, which would make it the deadliest attack on Kenya's army.
The Kenyan military has not given a death toll or responded to Gen Gurey.
In Nairobi, President Uhuru Kenyatta told a memorial service for the fallen soldiers that Kenyan troops would stay in Somalia despite the attack.
"We are at war with extremists, terrorists and it is a war we must win. We remain unbowed," Mr Kenyatta told the audience, which included families of the victims and some of the soldiers injured in the attack.
Gen Gurey, who commands Somali troops in the Gedo region, where the Kenyan army base is located in the town of El-Adde, told the BBC Somali service that the attack was foreshadowed by a build-up of militants in the area.
"We were told that Al-Shabaab was bringing fighters from all over the regions in south Somalia - from Gedo region, Middle and Lower Shabelle and Juba. They were very strong."
Kenya has said the bombs used by insurgents at the base were three times more powerful than that used in the 1998 US embassy attack in Nairobi, which killed 224 people.