Nairobi grenade attack: Al-Shabab denies Kenya blast
Somali Islamists have denied being behind Saturday's grenade blasts in the Kenyan capital Nairobi, in which at least six people were killed.
The militant al-Shabab "bears no responsibility whatsoever for the turbulence", a press release says.
Kenya's Internal Security Minister George Saitoti had accused the group of throwing four grenades from a passing car at a busy bus station.
Al-Shabab has threatened to attack Kenya after it sent troops to Somalia.
Police say four people have been arrested for Saturday's attack, which wounded more than 60.
"Al-Shabab has nothing to do with the hand grenade attacks that hit Nairobi," Sheik Mohamed Ibrahim, an official from the group, is reported as saying by the AFP news agency.
"We are not actually involved in such low-scale attacks," he said.
Mohammud Ali, from the BBC Somali Service, says al-Shabab is not usually shy about admitting when it is behind an attack.
The group has posted videos online of Kenyan officials they kidnapped in January from the border region.
But it has never claimed responsibility for any of the other explosions Kenyan authorities say it carried out in north-eastern Kenya in recent months.
Nor did it say it carried out a similar grenade attack in Nairobi in October - when grenades thrown into a bar and bus station killed one and injured many.
That attack happened just days after the Kenyan military had crossed into Somalia to fight the militants.
Saturday's attack occurred at about 19:30 local (16:30GMT) - one of the busiest times for commuters and shoppers, correspondents say.
The Daily Nation reports that a seventh person has died from his wounds - but this has not been confirmed.
After the explosions, a fire blazed in a small crater at the Machakos bus station and bystanders helped carry the wounded to ambulances, Reuters news agency said.
Kenyan Vice-President Kalonzo Musyoka later called for calm.
"This is an attack by people who think they can puncture the resolve of Kenyan people to fight against terror," Mr Musyoka told reporters on Sunday outside the Kenyatta hospital which is treating the injured.
"It is a difficult moment, but it should strengthen our resolve," he said.
There has been a string of small arms attacks and explosions on Kenyan soil ever since its troops crossed the Somali border.
Kenyan soldiers fighting al-Shabab in Somalia are due to be integrated into the African Union force next week.
The group has threatened to attack Kenya on several occasions.
Police there recently arrested several people over an alleged plot to blow up a hotel on the Kenyan coast.
Al-Shabab controls many southern and central parts of Somalia but is under pressure from a combination of forces from Kenya, Ethiopia and the African Union, which support the UN-backed government.