Kenyan police have linked the Al-Shabaab militant group to the Nairobi grenade attack that killed at least five people and wounded nearly 60 others on Saturday night.
"This is a cowardly act by Al-Shabaab elements," police spokesman Charles Owino told reporters at the Machakos country bus station, the site of the attack.
"But we will not relent in the war. We will get them and we will continue with the war."
Kenyan troops are currently fighting Al-Shabaab in neighbouring Somalia.
A spokesman at the city's main hospital, Kenyatta National Hospital, said at least seven other people were in a critical condition following the attack, in which witnesses reported seeing grenades thrown from a moving vehicle. (IN PICTURES: Blast rocks Kenyan capital)
Vice President Kalonzo Musyoka, while visiting survivors at the hospital, called for calm and reiterated that the Al-Shaabab militia would be dealt with.
"We urge for calm and we will definitely win the war against terrorism," he said.
This is the deadliest attack in Nairobi since the devastating August 1998 Al-Qaeda bomb attack on the US embassy that killed 213 people and injured 5,000.
Initial reports indicated that three people were killed and over 20 injured but later on Saturday, two others succumbed to their injuries in hospital and the number of those injured confirmed as 59.
A senior police official who did not want to be named told new agency AFP it was believed several grenades had been thrown towards the bus station.
Witness Charles Njenga said: "I just saw a vehicle pass and then someone just threw things that exploded. Many people have been injured."
"I survived because I was in a bus that people were still boarding," he added. Other witnesses spoke of three or four grenades having been thrown in and around the bus station from a moving vehicle.
Traces of blood were still visible at the bus station, where around 10 buses were parked, and ambulances ferrying the wounded to hospital. Others, less seriously injured, were being treated on the spot.
About 500 metres from the bus station, the body of one of the victims, a young man, lay on the ground. "I came to get petrol when I saw a man who was running collapse on the ground," said Reuben Otela, a motorcyclist.
"When I got closer, I saw that he was covered in blood," he added.
It is the first such incident in the Kenyan capital since two grenade attacks carried out within 24 hours of each other in October last year, that killed one person and injured 30 others.
The first of those attacks targeted a bar in the capital; the second was an attack on a bus stop.
A Kenyan supporter of Somalia's Islamist al-Shabaab fighters was arrested soon afterwards and convicted after having confessed to the attacks.
No one has so far claimed responsibility for Saturday's killings. But the Al-Shabaab have on several occasions threatened reprisal attacks against Kenya since its troops went over the border into southern Somalia in mid-October. (Read: Kenya warns of Shabaab threat at borders)
Kenya sent its soldiers, backed by planes and helicopters, into Somalia following the abduction of several foreigners on Kenyan soil -- although the al-Shabaab have denied any involvement in the kidnappings.