Islamist al Shabaab militants killed 36 non-Muslim workers at a quarry in northeast Kenya on Tuesday, beheading at least two of them in revenge for Kenyan military action against the group in neighboring Somalia.
The gunmen crept up on dozens of workers sleeping in tents at about 1 a.m. (2200 GMT), a resident said, in the same area near the Somali border where they hijacked a bus and killed 28 passengers just over a week ago.
"The militia separated the Muslims, then ordered the non-Muslims to lie down where they shot them on the head at close range," Hassan Duba, an elder at a nearby village, said.
A witness said at least two of the victims were beheaded in the latest in a string of attacks that are piling pressure on Kenyan President Uhuru Kenyatta over national security. His office said he would address the nation later in the day.
As with past attacks, al Shabaab militants said they were 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 attacked 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.
Photos posted on Twitter and other social media websites showed a line of men lying face down on rocky ground.
Critics say the president has not done enough to secure the nation since al Shabaab gunmen attacked Nairobi's Westgate shopping mall last year, killing 67 people.
Western diplomats say Kenya's security services, which receive support from Britain, the United States and others, are hobbled by poor coordination and there has been little sign of reform.
"It makes you curious if there is really an appetite or desire for anything to change," said one diplomat.
Government opponents say the troops in Somalia have not protected Kenya and should be withdrawn.
"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.
The government has promised to step up security, but the public has grown increasingly frustrated and, after the Mandera bus attack, small protests have been staged demanding action.
Al Shabaab have 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."
News of the quarry attack sent the Kenyan shilling lower against the dollar early on Tuesday. The currency has been under pressure in part because tourism, a major source of foreign exchange, has been battered by the spate of attacks. (Additional reporting by Joseph Akwiri in Mombasa, Duncan Miriri, Edith Honan in Nairobi and Feisal Omar in Mogadishu; Editing by Louise Ireland and Andrew Heavens)