Grenade blast sows chaos at Nairobi church, one dead- AFP:

NAIROBI — A man set off a grenade during a church service in the Kenyan capital Nairobi on Sunday, sowing chaos and killing one worshipper.

"It was horrible. People were screaming all over and blood was all over," resident Samuel Kimani Mwandati said outside the God's House of Miracles Church in Nairobi's Ngara neighbourhood.

The area police chief, Joseph Gichangi, said there had been "one fatality," and later police estimates put the number of injured at 15.

Nairobi has been hit by a series of unclaimed blasts since late 2011, which Kenyan officials have blamed on Somalia's Al-Qaeda-linked Shebab Islamists.

Kenyan troops launched an incursion into neighbouring Somalia in October to increase the military pressure against the Shebab, and the Islamists have vowed revenge attacks so long as Kenyan forces remain on Somali land.

"We have not known the motive of the attack, but we can't rule out anything," said Nairobi deputy police chief Moses Nyakwama.

Gichangi said the assailant was reportedly a member of the congregation and fled immediately after setting off the grenade. Witnesses said he was armed.

"We saw a man running out after the blast and when we chased him he pointed a pistol at us, so we ran back," Kennedy Wasilwa recounted.

Joseph Kimani, who owns a shop nearby, told AFP he rushed to the church after hearing "a loud blast," and initially thought the church had caught fire.

"Then I found people screaming and some were trying to assist others who had injuries," he said.

Inside the church a young man lay motionless, Mwandati recounted. "We knew he was dead or seriously injured. He is the one who has died."

The Vatican condemned the violence.

"The new terrorist attacks in Kenya and Nigeria at Christian celebrations are horrible and despicable acts," Vatican spokesman Federico Lombardi said.

Attackers armed with bombs and guns opened fire at church services in a Nigerian university on Sunday, killing around 20 people.

Police said witnesses provided a description of the attacker and urged the community to assist their investigation.

"With the help of the public, we will get him," Nyakwama said.

A March 10 blast at a Nairobi bus terminal killed nine people and injured around 60, while on March 31 another person died at a church gathering in the coastal town of Mtwapa.

Interior Minister George Saitoti blamed the Shebab for the blast, although the Islamists did not claim it.

Nairobi launched its operation in Somalia following a spate of kidnappings in Kenya that officials blamed on the Islamist rebels.

Earlier this month, the Shebab threatened retribution and revenge for the continued presence of Kenyan troops on Somali land.

"The Kenyan public must be aware that the more Kenyan troops continue to persecute innocent Muslims of Somalia, the less secure Kenyan cities will be," the Islamists said in a statement. "Such is the law of retribution."

The Shebab once controlled vast swathes of Somali territory but have in recent months been chased out of most of their strongholds.

The Western-backed African Union force in Mogadishu along with the Kenyan and Ethiopian armies have increased military pressure against the Islamist rebels on three fronts.