Kenyan police say it is “rather unlikely” a deadly grenade attack at a downtown Nairobi church is linked to the Islamist militant group al-Shabab.

Officials say the attack on Sunday at God's House of Miracles International Church killed one person and wounded 16 others.

Police spokesman Eric Kiraithe told VOA the armed attacker walked into the church posing as a worshipper, hurled the grenade and then fled.

“”He ran out of the church. He was pursued, but he was armed with a handgun and fired at those who were pursuing him.”

Authorities say they have a detailed description of the suspect, who escaped.

Police are investigating the motive behind the attack and cautioned it should be not seen the result of sectarian or militant violence.

Kiraithe says there is an indication the attack may be related to “internal strife” within the church. He did not elaborate.

There have been a string of similar attacks in Kenya this after, after Kenya sent troops into neighboring Somalia to fight the al-Qaida-allied group al-Shabab.

Al-Shabab has vowed to seek revenge by launching attacks on Kenyan soil

Last week, the U.S. embassy in Nairobi warned it had “credible” information” that attacks were being planned against hotels and government buildings in the capital.

Kiraithe told VOA he said “serious doubts” Sunday's attack is connected to the U.S. embassy's warning.