Kenyan police said on Monday they are questioning several people in connection with Monday's explosion which killed at least one person and left more than 30 others injured in Kenya's capital of Nairobi.
Police spokesman Eric Kiraithe said among those being questioned, there is a taxi driver who ferried three men to the scene of the explosion.
"We are questioning several people in connection with this blast. We are also interviewing several others to be able to ascertain the cause of the blast which went off this morning," Kiraithe told Xinhua by telephone.
"A postmortem is being conducted to assist in investigations over the precise cause of death and samples will be sent for further investigations both in local and foreign laboratories, " said Kiraithe.
"So far debris from the scene is being examined for traces of explosives. Initial investigations show that the source of the explosion was extremely small."
The taxi driver was arrested moments after the 8 a.m.(0500 GMT) explosion that occurred outside a restaurant near a three-Star Ambassador Hotel in the center of the city.
Investigators said witnesses and other taxi operators assisted police to locate the driver in a different part of the city center. Initial reports suggested a suicide bomber carried out the attack but this has not been confirmed by the police.
The area has been sealed off by police and the military. The blast was close to the site of the 1998 U.S. embassy bombing.
Anti-terrorist police experts confirmed the explosives were deliberately assembled for a mission, which was yet to be established and it is believed that the lead criminal was killed and his accomplice seriously injured. He is among those admitted to hospital.
Eyewitness James Mwangi reported seeing two bodies and some rip- off limbs at the scene.
"There was a man who had dropped from a bus and then headed into a restaurant with a polythene paper bag in his hands. The guards stopped him from entering the restaurant because he was wearing something that looked suspicious," Mwangi told The Daily Express at the scene.
"It was after this altercation that a loud explosion occurred. I could see personal items and window glasses strewn all over the place. Initially I thought it was a tyre burst but it was louder than that," he said.
But the police spokesman cautioned Kenyans to avoid speculation and give them time to establish the cause of the blast which caused panic along the busy terminus used by public service vehicles plying several city routes. Most of the injured were caught up as they waited for transport to various city destinations.
A witness told police that the taxi driver made a U-turn after dropping three men at the bus stop. Then the three tried to board a bus that was destined for the Jomo Kenyatta International Airport but did not do so because it was full.
The three then engaged a shoe shiner in a conversation near the entrance to the City Gate Restaurant and one of the men reportedly placed a bag he was carrying on the ground as they talked.
A man who was sweeping the verandah asked the owner of the bag to remove it.
"But the owner of the bag started moving back as the sweeper ordered him to remove it," said a witness."It was at that time that something in the bag exploded,"said the witness.
Shop windows nearby and papers were shattered and the area has now been cordoned off as anti-terrorist police with sniffer dogs combed the scene for further explosives.
"After the blast people just started screaming and running all over. At one point, a lady who was at the center of the chaos was blown across the street and we went to assist her. We covered her body as her clothes had been torn off," said an eyewitness.
Doctors at the Kenyatta National Hospital (KNH) said they have received at least 31 victims of the blast who are under treatment.
"So far we have received 31 patients who were injured at the site of the incident. Some of them have lost blood and have fractured limbs. Six are in serious condition," said Kariuki Chege, KNH spokesman.
Nairobi was last hit by bomb in 1998 when the United States embassy in the downtown was brought down.