Kenya is marking a year since the attack on a Nairobi shopping centre, in which at least 67 people were killed.
A memorial plaque with names of the victims was unveiled ahead of a candle-lit vigil being held later on Sunday.
The siege at Westgate lasted four days, with CCTV footage showing terrified shoppers fleeing the gunmen and cowering behind counters.
Somali Islamist group al-Shabab said it carried out the attack in response to Kenya's military operations in Somalia.
On high alert
Relatives of the victims laid wreaths at a garden in the forest where 67 trees were planted after the attack.
Interfaith prayers were held at the site as a memorial plaque with names of the victims on was unveiled.
Amul Shah, who spoke at the event, said his life was "completely shattered" after his son Mitul died in the attack.
Mr Shah said his 38-year-old son was looking after children taking part in a cooking competition on the shopping centre's rooftop when the siege happened.
"He helped several children escape from the attack, but he was not lucky himself. He was so selfless," Mr Shah said.
Ahead of the commemorations, Kenya was put on high alert amid fears of possible attacks by militants.
"We are prepared in case of anything. Specialised units are on the ground and we have intensified patrols during this period of the anniversary," Kenyan police chief David Kimaiyo said.
Last year's attack sparked a four-day siege in which large parts of the shopping centre were destroyed amid heavy fighting and a fire.
All four gunmen are believed to have died during the assault.
The Kenyan authorities have been criticised for what is seen by some analysts as their slow response to the attack and also lack of co-ordination between police and the army. Kenya rejects the claims.
At the scene: BBC's Anne Soy, Nairobi
Dressed in T-shirts bearing his smiling portrait, Mitul Shah's family no doubt took time to prepare for the first anniversary of the Westgate attack.
Tears rolled down his parents' cheeks as they fondly remembered their only son.
Some families broke down as they lay flowers at the Amani Garden. Amani means peace in Swahili.
Sixty-seven trees were planted a month after the attack to symbolise each of those who died. A young girl said: "My uncle is here", as she watered the tree bearing the name Crispal Gaitungu.
The friends and families of the victims unveiled a plaque with the names of the departed.
Some survivors were also present. Sergeant Moses Emojong, one of the first officers to respond to what was at first thought to be a robbery, survived 15 gun shots. He now walks on crutches.
"The fact that I'm talking to you today reminds me that I'm alive," he said.
Four Somalis are being held in prison in Kenya on terrorism charges linked to the attack.
Al-Shabab is fighting to create an Islamic state in Somalia and is banned as a terrorist group by both the US and the UK.
Earlier this month, al-Shabab leader Ahmed Abdi Godane was assassinated in US air strikes in southern Somalia.
The militants later chose a new chief and vowed revenge attacks.