Nairobi blast was a bomb attack - Kenya police

NAIROBI (Reuters) - An explosion that wounded more than 30 people when it tore through a trading centre in the heart of the Kenyan capital on Monday was caused by a bomb, Kenyan police said on Tuesday.

There has been no claim of responsibility for the attack, though suspicions will fall on Somali Islamist militants and their sympathisers blamed for a string of attacks in Kenya since Nairobi sent troops into southern Somalia in October last year.

An initial statement by the police chief that an electrical fault might have been to blame sparked widespread derision.

"Investigators have now concluded that the explosion was caused by an improvised explosive device planted in the building by criminal elements," police spokesman Eric Kiraithe said in a statement.

Prime Minister Raila Odinga was quick on Monday to denounce the attack as a "heinous act" and said Kenyans would not be cowed by "terrorists".

Kiraithe said the police were zeroing in on two male suspects and released a photo fit of a man they identified as Emrah Erdogan who they said was believed to be a Turkish or German national.

Erdogan is alleged to have entered Kenya on May 3 and is thought to still be in the east African country.

Kenyan counter-terrorism police and Western security agents were seen on Monday removing samples from the blast site.

Agents from the United States' Federal Bureau of Investigations have assisted Kenyan authorities in the aftermath of attacks in the past.

Two witnesses told Reuters they had seen a man drop a black bag inside the building moments before the blast which ripped open the roof, sent shards of glass flying through the air and ignited a fire that sent smoke billowing into the air.

"The team has been able to recover several materials from the scene of the explosion which have been sent for forensic analysis to determine the composition of the explosive and its method of initiation," Kiraithe said.

(Reporting by Humphrey Malalo; Editing by Richard Lough and Jon Hemming)