Kenyan President Uhuru Kenyatta on Saturday declared three days of national mourning after Somali Islamist militant group al Shabaab gunmen entered a university campus and killed almost 150 people in one of the country’s worst massacres.

“I declare three days of mourning during which our flags will fly at half mast,” Kenyatta said in a televised national address from the capital Nairobi, condemning the “barbaric slaughter” in his first address since the attack ended on Thursday.

The leader also warned that planners and financiers of attacks like the one that took place in Garissa town are “deeply embedded in our communities”.

Kenyatta said his administration would “respond in the severest ways possible” to the Garissa attack, which occurred Thursday when four gunmen entered a campus and slaughtered students. The military moved in hours later and the gunmen were killed.

“We will fight terrorism to the end,” said Kenyatta. “I want you to know that our security forces are pursuing the remaining accomplices. We will bring all of them to justice … We are also in active pursuit of the mastermind (of the attack) and have placed a reward for his capture,” he said.

Kenyatta urged survivors of the attack “to continue working hard in their education”.

Kenyatta’s nationwide address came after al Shabaab warned of more attacks in Kenya.

“Kenyan cities will run red with blood,” said al Shabaab according to the SITE intelligence monitoring group.

The Islamic militants said the attack on Garissa University College was in retaliation for killings carried out by Kenyan troops fighting the rebels in Somalia.

“This will be a long, gruesome war of which you, the Kenyan public, are its first casualties,” said the statement, issued on Shabaab-affiliated websites and Twitter accounts.

“No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath,” it said.

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