Pope Francis told Christian and Muslim leaders in Kenya they have no choice but to engage in dialogue to prevent the "barbarous" Islamic extremist attacks that have struck the country recently.

On his first full day in Africa, Pope Francis insisted religion can never be used to justify violence.

He lamented that "all too often, young people are being radicalised in the name of religion to sow discord and fear, and to tear at the very fabric of our societies".

The pope said interfaith dialogue is not a luxury or optional, but is simply "essential".

Pope Francis made the comments as he met Kenyan faith leaders at the start of a busy day that will see him celebrate Mass on a rain-soaked university campus and deliver a major environment speech.

Kenya, a former British colony is majority Christian, but Muslims represent about 10% of the population.

In his remarks, Pope Francis referred explicitly to three recent attacks claimed by the Somalia-based al-Shabab extremist group, saying he knew well that the memories were still fresh in Kenya's mind.

In April, the al-Qaida-linked al-Shabab claimed responsibility for an attack on a mostly Christian college in north-eastern Kenya that left some 150 people dead.

A month earlier, al-Shabab claimed responsibility for attacks in Mandera county on the Somali border in which 12 people died. In September 2013, at least 67 people were killed in an attack by al-Shabab on the Westgate mall in Nairobi.

Al-Shabab opposes Kenya's decision to send troops to Somalia to fight the group as part of an African Union force backing Somalia's weak government.

"Here, I think of the importance of our common conviction that the God whom we seek to serve is a God of peace," the Pope said.

"How important it is that we be seen as prophets of peace, peacemakers who invite others to live in peace, harmony and mutual respect."