Kenyan President Uhuru Kenyatta has said "we will not flinch" in the war against Islamist group al-Shabab after a massacre near the Somali border.

"This is a war against Kenya and Kenyans," he said on national TV. "It is a war that every one of us must fight."

Kenya's police chief, David Kimayo, and Interior Minister Ole Lenku are being replaced.

Al-Shabab earlier killed 36 quarry workers in the Mandera region.

The group attacked the workers around midnight on Monday as they slept in tents at the quarry in Kormey, 15km (nine miles) from the north-eastern town of Mandera.

The non-Muslim workers were shot dead after being separated from the Muslims.

A driver who visited the scene of the attack, Ali Sheikh Yusuf, told the BBC most of the victims appeared to have been lined up, and shot in the head, at close range.

He said four were beheaded inside their tents, while three appeared to have escaped to Mandera town.

Al-Shabab has stepped up its campaign in Kenya since 2011, when Kenya sent troops across the border to help battle the militants.

Only last week, al-Shabab killed 28 people in an attack on a bus targeting non-Muslims in the same area.

In one of the worst attacks on Kenyan soil, 67 people were killed last year when four gunmen took over the Westgate shopping mall in Nairobi.

In recent months, dozens of people have been killed in a series of shooting attacks in coastal districts.

The security situation has led to calls from the opposition and some in the governing party for the dismissal of Interior Minister Joseph Ole Lenku and police chief David Kimaiyo.

Hundreds of people sought refuge at a military airstrip in the Mandera region last week, fearing a fresh assault by al-Shabab.