The son of a Kenyan government official was one of the masked gunmen who killed nearly 150 at a university last week, the interior ministry said on Sunday, as Kenyan churches hired armed guards to protect their Easter congregations.

Interior Ministry spokesman Mwenda Njoka said Abdirahim Abdullahi, son of a government official in the northern Mandera county bordering Somalia, was one of four gunmen who stormed the college campus in northeastern town of Garissa.

"The father had reported to security agents that his son had disappeared from home ... and was helping the police try to trace his son by the time the Garissa terror attack happened," Njoka told Reuters in a text message.

President Uhuru Kenyatta on Saturday said the planners and financiers of attacks were "deeply embedded" within Kenyan communities and urged Muslims to do more to fight radicalization.

A Garissa-based official said the government was aware Abdullahi, a former University of Nairobi law student, had joined the group Al Shabab after graduating in 2013.

"He was a very brilliant student. But then he got these crazy ideas," said the official.

Al Shabab group said the assault on Garissa, some 120 miles from the Somali border, was revenge for Kenya sending troops into Somalia to fight alongside African Union peacekeepers against the Al-Qaeda-aligned group.

The fighters have threatened to turn Kenyan cities "red with blood" and police have stepped up security at shopping malls and public buildings in the capital Nairobi, and the eastern coastal region which has been prone to Al Shabab attacks.

The Garissa assault has further strained the historically cordial relations between Kenya's Christian and Muslim communities, which have deteriorated due to frequent attacks on Christian priests and churches.

In Nairobi's Holy Family Basilica cathedral, two uniformed police officers armed with AK-47 rifles manned the entrance gate. One officer said more plain clothes officers were inside.

"Everyone is anxious and you never know what will happen next, but we believe the biggest protector is God and we are praying," said Samuel Wanje, 27, a youth member at the church.

Pope Francis decried Thursday's attack in his Easter Sunday service, praying for those killed by gunmen who hunted down Christians while sparing Muslims.

At one church in the Indian Ocean port city of Mombasa, worshipers were evacuated and a bomb disposal unit deployed due to a suspicious vehicle parked outside the church.

Kenyan priests said they feared churches could be targeted on Easter Sunday, the main liturgical feast in the Christian calendar.

"We are very concerned about the security of our churches and worshipers, especially this Easter period, and also because it is clear that these attackers are targeting Christians," Willybard Lagho, a Mombasa-based Catholic priest and chairman of the Coast Interfaith Council of Clerics (CICC), told Reuters.

He said churches Mombasa were hiring armed police and private security guards for mass on Easter Sunday. Christians make up 83 percent of Kenya's population of 44 million.

Reuters