By Edmund Blair and Edith Honan
NAIROBI (Reuters) - Somali al Shabaab Islamist militants killed 36 non-Muslim workers at a quarry in northeast Kenya on Tuesday, prompting the president to sweep out his top security officials in order to tackle a relentless wave of violence.
Kenyans have grown increasingly critical of President Uhuru Kenyatta for failing to do more to defend the east African nation from the incessant militant attacks, which have killed well over 200 people since 2013.
Al Shabaab has claimed responsibility for much of the bloodshed and says it will keep it up to persuade Kenya to pull its troops out of neighboring Somalia, where its forces have joined other African Union troops battling the militants.
In Tuesday's attack, gunmen crept up on dozens of workers sleeping in tents, a resident said, in the same area near the Somali border where a bus was hijacked just over a week ago and 28 passengers killed.
"The militia separated the Muslims, then ordered the non-Muslims to lie down where they shot them in the head at close range," said Hassan Duba, an elder at a nearby village.
A witness said at least two of the victims were beheaded.
Public pressure had been rising on Kenyatta to sack police chief David Kimaiyo and Interior Minister Joseph ole Lenku since al Shabaab's attack on Nairobi's Westgate shopping mall last year that killed 67 people, and after subsequent violence.
Addressing the nation on Tuesday, Kenyatta said he had accepted Kimaiyo's resignation and nominated a new interior minister, Joseph Nkaissery, a retired major general, urging parliament to speedily approve his choice.
He called on opponents, who have criticized his handling of security policy, to unite in fighting the militants. "Our bickering only emboldens the enemy," the president said.
As with past attacks, al Shabaab said it was punishing Kenya for sending troops to join African peacekeepers battling the Islamists in Somalia. In a statement, it put the death toll at 40 and called the victims "Kenyan crusaders".
"We are uncompromising in our beliefs, relentless in our pursuit, ruthless against the disbelievers and we will do whatever necessary to defend our Muslim brethren suffering from Kenya’s aggression," spokesman Ali Mohamud Rage said.
Kenya's government and a witness said 36 people were killed. The government cited survivors saying about 20 fighters assaulted the quarry, about 15 km (10 miles) from the town of Mandera. One person died in another attack on the northern town of Wajir late on Monday.
Fearing another attack, hundreds of people in Mandera fled to army or police posts for shelter. "I am on my way out of Mandera. I can't wait to be ferried in a coffin or body bag," said one government worker, giving his name only as George.
Western diplomats say that Kenya's security services, which receive support from Britain, the United States and others, are hobbled by poor coordination.
Government opponents say the troops in Somalia have not protected Kenya and should be withdrawn. The government has repeatedly said it will not pull the troops out.
"They were supposed to create a buffer between our countries and the chaos on the other side. But it has not done that. So we are saying, 'Leave'," Dennis Onyango, a spokesman for opposition politician and former prime minister Raila Odinga, said.
Al Shabaab has been driven out of several strongholds in Somalia by an offensive by African Union and Somali troops this year, but analysts said it would not prevent the group from carrying out guerrilla-style attacks or striking abroad.
"This (latest attack) seems very much in line with al Shabaab strategy," said Cedric Barnes of the Crisis Group in Nairobi of the latest attack. "It's partly a result of al Shabaab being squeezed in Somalia."
(Additional reporting by Joseph Akwiri in Mombasa, Duncan Miriri, James Macharia and Drazen Jorgic in Nairobi, Noor Ali in Isiolo and Feisal Omar in Mogadishu; Writing by Edmund Blair; Editing by James Macharia and Mark Heinrich)