A grenade explosion inside a crowded church in the Kenyan capital has killed one person and injured 15 others, police say.

Witnesses reported a man walked into the God's House of Miracles International Church in Nairobi, released the grenade and fled.

"The church was absolutely packed for Sunday service this morning and someone who was posing as a worshipper apparently lobbed a grenade into the crowd and then took off on foot," CBC's Carolyn Dunn reported from Nairobi. 

Steven Mulinge, a church pianist who was among the wounded, recalled seeing a man walking through the entrance and hurling what looked like a stone at the altar.

"I heard a blast and then around me everyone was covered in blood," he said. "Later I found myself lying down with a deep cut on my hip."

Some of the 50 church members in attendance said they suspected the attack was related to an unresolved land dispute.

James Maina, who described himself as a church elder, said his church may have been targeted by neighbours who claim to own the land on which it is built. He said the church had suffered minor attacks in the past, including having its windows smashed.

String of attacks

Earlier, police said the hand grenade is a hallmark weapon of past attacks by al-Qaeda-linked al-Shabab militants from Somalia.

"It was the latest in a string of grenade attacks that have happened in Nairobi and elsewhere in Kenya," Dunn said. "At least eight people have been killed by grenades thrown in public places, including a crowded bus stop in the capital last month."

"Al-Shabab has been warning of attacks and has claimed responsibility for previous attacks carried out since the Kenyan military launched operations inside Somalia in October," Dunn said.

Sunday's deadly explosion follows a U.S. Embassy warning that a terror attack on prominent government buildings and hotels in Nairobi could be imminent.

The embassy said Monday that the timing of the attack is not known but they believe it to be at a final planning stage.

"That [statement] was enough for Canada to follow suit with a warning to folks living in Nairobi from Canada to exercise a really high degree of caution.

"It's not clear whether those warnings and today's grenade attack are in any way related," Dunn said.

Police have said al-Shabab is suspected of killing at least 30 Kenyan civilians since Kenyan troops entered Somalia.

In February, police spokesman Eric Kiraithe said the killings are believed to have been carried out by sympathizers of al-Shabab in Kenya.

He said most of the attacks were carried out in towns near the border between Somalia and Kenya.

With files from The Associated Press