(CNN) Their M.O. is a tried and terrifying one: Launch a raid, single out Christians, and then spray them with bullets.

But when Al-Shabaab militants ambushed a bus Monday, things didn't go according to plan.

A group of Kenyan Muslims shielded the Christian passengers and told the attackers they were prepared to die together.

The Muslim passengers, who were mostly women, told the Islamic militants to kill them all or leave them alone, witnesses said.

Police escort breaks down

The bus was headed to the city of Mandera, near the border with Somalia and Ethiopia.

The journey is such a security risk that most buses travel with a police escort.

In this case, however, the police car broke down and the bus continued on its journey, Joseph Nkaissery, Kenya's interior cabinet secretary, said.

A few hours later, the militants attacked.

Brutal acts

Al-Shabaab, a Somali group the United States has designated as a foreign terrorist organization , wants to turn Somalia into a fundamentalist Islamic state. It has launched a series of attacks in Kenya, since Kenyan forces went into Somalia to battle the extremists in 2011.

Its goal: sow division in the border regions of Kenya and Somalia, where many of the people are ethnically Somali, analysts say.

Among Al-Shabaab's most brutal acts was the raid on Garissa University College in April that left nearly 150 people dead. Witnesses described how gunmen asked students to recite verses from the Quran. If they couldn't, they were killed.

Photos: Attack at Kenyan university Photos: Attack at Kenyan university A relative grieves after identifying a body at a funeral home in Nairobi, Kenya, on April 6, 2015. Several days earlier, gunmen stormed Garissa University College in Garissa, Kenya, and killed at least 147 people. The Somalia-based Al-Shabaab militant group claimed responsibility for the assault. Hide Caption 1 of 24 Photos: Attack at Kenyan university Abandoned shoes remain at the scene of the attack on April 6, 2015. Hide Caption 2 of 24 Photos: Attack at Kenyan university A nun prays during an Easter service at a Garissa church on April 5, 2015. Hide Caption 3 of 24 Photos: Attack at Kenyan university People in Garissa crowd around a mortuary window on April 4, 2015, to view the bodies of the alleged attackers. Authorities later paraded the bodies through a crowd on the bed of a pickup truck. Hide Caption 4 of 24 Photos: Attack at Kenyan university Members of the public view the bodies of the alleged attackers on April 4, 2015. Hide Caption 5 of 24 Photos: Attack at Kenyan university Survivor Cynthia Cheroitich speaks to a television reporter at a hospital ward in Garissa on April 4, 2015. Cheroitich told CNN she hid in a closet, covering herself. Hide Caption 6 of 24 Photos: Attack at Kenyan university Students mourn the victims on April 3, 2015. Hide Caption 7 of 24 Photos: Attack at Kenyan university Students get on a bus at the gate of the school on April 3, 2015. Hide Caption 8 of 24 Photos: Attack at Kenyan university Students listen to an address by Joseph Nkaissery, Kenya's interior minister, on April 3, 2015. He vowed that the country would not bow to terrorist threats. Hide Caption 9 of 24 Photos: Attack at Kenyan university A Kenyan soldier stands guard in Garissa on April 2, 2015. Hide Caption 10 of 24 Photos: Attack at Kenyan university A woman is helped away from the building where she had been held hostage at the school. Hide Caption 11 of 24 Photos: Attack at Kenyan university A student hostage is escorted out of the school after troops ended the gunmen's siege on April 2, 2015. Hide Caption 12 of 24 Photos: Attack at Kenyan university Kenyan soldiers take cover as heavy gunfire continues in front of the school on April 2, 2015. Hide Caption 13 of 24 Photos: Attack at Kenyan university Kenyan soldiers take cover as shots are fired in front of the university on April 2, 2015. Hide Caption 14 of 24 Photos: Attack at Kenyan university A local resident shows a bullet allegedly from the militants in front of the school. Hide Caption 15 of 24 Photos: Attack at Kenyan university Members of the Kenyan Red Cross gather outside a hospital in Nairobi to receive victims of the attack on April 2, 2015. Hide Caption 16 of 24 Photos: Attack at Kenyan university Kenyan soldiers stand guard in front of the school on April 2, 2015. Hide Caption 17 of 24 Photos: Attack at Kenyan university A Kenyan soldier takes cover as shots are fired in front of the school on April 2, 2015. Hide Caption 18 of 24 Photos: Attack at Kenyan university Students take shelter in a vehicle after fleeing the attack. Hide Caption 19 of 24 Photos: Attack at Kenyan university Students step out of a house in Garissa where they sought refuge after escaping the attack. Hide Caption 20 of 24 Photos: Attack at Kenyan university Police officers take positions outside the school as an ambulance carries victims to a hospital in Garissa. Hide Caption 21 of 24 Photos: Attack at Kenyan university Students leave a house where they had taken shelter on April 2, 2015. Hide Caption 22 of 24 Photos: Attack at Kenyan university Local residents donate blood at a hospital in Garissa on April 2, 2015. Hide Caption 23 of 24 Photos: Attack at Kenyan university Kenyan police take cover outside the school during the attack. Hide Caption 24 of 24

The group regularly storms buses, particularly this time of the year -- one of the busiest travel seasons in the nation. Throngs make their way to relatives' homes for the holidays, with buses and other public transportation packed.

In one such attack last year , they raided a bus and shot dead 28 people who failed to recite Quran verses.

'We are not separated by religion'

In the Monday attack, the gunmen ordered Muslim passengers to come out of the bus and separate themselves from the Christians.

There were more than 100 passengers on board.

The Muslim passengers refused.

They gave the Christian women their hijabs and helped others hide behind bags in the bus, passenger Abdiqafar Teno told CNN.

"They told them, 'If you want to kill us, then kill us. There are no Christians here," he said.

A Christian man who tried to run away was captured and shot dead, Teno said. The driver of a truck, which was trailing the bus, was also killed.

Photos: Leaders of deadliest terrorist groups Photos: Leaders of deadliest terrorist groups Mawlawi Haibatullah Akhunzada, named the new Afghan Taliban leader following the death of Mullah Akhtar Mohammad Mansour, is in his late 50s and comes from Panjwai district of southern Kandahar province. Hide Caption 1 of 7 Photos: Leaders of deadliest terrorist groups Ayman Al-Zawahiri is the leader of al Qaeda. He previously acted as Osama bin Laden's personal physician and is believed to have played an important role in the September 11 terror attacks. Hide Caption 2 of 7 Photos: Leaders of deadliest terrorist groups Abu Bakr al-Baghdadi is the leader of ISIS, the militant group that wants to create an Islamic state across areas of Iraq and Syria. Not much is known about the ruthless leader. A reward of up to $10 million has been offered by the U.S. government. Hide Caption 3 of 7 Photos: Leaders of deadliest terrorist groups Qasm al-Rimi is the leader of al Qaeda in the Arabian Peninsula. He succeeded Nasir al-Wuhayshi, who was killed in a drone strike . Al-Rimi has spent more than a decade at the helm of the military side of AQAP, and he also plans their large international operations. Hide Caption 4 of 7 Photos: Leaders of deadliest terrorist groups Mullah Fazlullah is the leader of the Pakistani Taliban. The group, which has links to the Afghan Taliban and al Qaeda, has claimed responsibility for shooting teen activist Malala Yousafzai and attempting to detonate a car bomb in New York's Times Square in 2010. Hide Caption 5 of 7 Photos: Leaders of deadliest terrorist groups Ahmed Omar Abu Ubaidah is the leader of al-Shabaab, an al Qaeda-linked militant group based in Somalia. Little is known about the man characterized as a low-ranking commander. Hide Caption 6 of 7 Photos: Leaders of deadliest terrorist groups Abubakar Shekau is the leader of Boko Haram, a militant Islamic group working out of Nigeria. Little is known about the religious scholar. He operates in the shadows, leaving his underlings to orchestrate his mandates. A reward of up to $7 million has been offered by the U.S. government. Hide Caption 7 of 7

The gunmen left, but warned they would return.

Nkaissery, the interior cabinet secretary, told reporters security forces were in "hot pursuit of the criminals."

Then he commended the actions of the Muslim passengers.

"We are all Kenyans, we are not separated by religion," he said. "We are one people as a nation. And this is a very good message from my brothers and sisters from the Muslim community."