Islamic extremist gunmen from neighboring Somalia killed 12 people in an attack on non-Muslims in Kenya's northern Mandera County, an official said Tuesday.

Somalia's al-Shabab rebels claimed responsibility for the early-morning attack on the Bishaaro Guest House, saying its fighters targeted Christians, according to the group's Andalus radio station.

The gunmen used grenades and homemade explosives to break into the guest house and then stormed in with guns, said Mohamed Saleh, Mandera's regional commander.

Survivor Veronica Wambui, an actor with a group touring Mandera to showcase textbooks in schools, said they were asleep at around 2:30 a.m. when they heard explosions at the main gate.

The attackers went room to room shooting and killing her colleagues, she said. She said she and others hid in a storeroom and the attackers set off another explosion which made the wall collapse on her.

"I could see the lights from the torch (flashlight) when they were checking out the room, but the collapsed wall had covered me," said Wambui, speaking from her hospital bed where she was being treated for a bullet wound in her left hand and injuries to her legs.

Two weeks ago, a watchman was killed at the guest house and there were rumors that the lodging was being targeted.

Al-Shabab has vowed retribution on Kenya for sending troops to Somalia since 2011 to fight the extremists, who are waging an insurgency against Somalia's weak, Western-backed government.

Al-Shabab extremists hijacked a bus in Mandera in November 2014 and killed 28 non-Muslims on board. In December 2014, they killed 36 quarry workers. This year, six people were killed in July when gunmen shot at buses. On Oct. 6, al-Shabab gunmen killed six at a residential compound housing non-Muslims.

Al-Shabab's campaign targeting non-Muslims has had a devastating impact on education in Mandera. Many non-Muslim teachers have asked to be transferred from the region, causing a shortage of teachers.