Twelve people have been killed in an attack in north-east Kenya believed to have been carried out by the Somali Islamist group Al-Shabaab.

Media outlets sympathetic to the group reported that the latest incident “killed Christian Kenyans” who were not from the local area.

Police in the town of Mandera, which lies on the border with Somalia, said the attackers used improvised explosive devices to break the metallic doors and enter the Bishaaro Hotel, before shooting 12 people dead in their rooms.

Ten of the victims were visiting the town to stage performances in schools relating to books on the curriculum, according to the Daily Nation newspaper.

Al-Shabaab has carried out many attacks targeting Christians in the mainly-Muslim border region. Earlier this month, militants shot dead six people in a night-time attack the group said was aimed at forcing Christians to leave the area.

The commissioner of Mandera County, Fredrick Shisia, claimed Al-Shabaab is receiving funding from Kenyan businessmen.

Shisia said the government had received intelligence that the group was extorting taxes and protection money from businesses in Mandera. However, he said that anyone making such payments would be punished, and accused them of undermining the government’s efforts to combat terrorism.

“Anyone who is in communication with members of Al-Shabaab will be arrested and charged,” he said.

Critics have accused the Kenyan government of failing to prevent the attacks and being slow to implement measures that would improve security, such as a more consistent electricity supply that could provide more consistent lighting.

The attack earlier this month, in which six people died, took place at a gated residential building, many of whose 33 residents had moved to Mandera for work.

However, it is not clear how many of the dead were Christians. According to Kenyan media, three were quarry workers, two worked for a Muslim relief agency and one was a barber. (Al-Shabaab’s own radio station had claimed at the time it had “killed six Christians”.)

The quarry workers were John Ndegwa, Martin Munene and Duncan Ndegwa and the NGO workers were Evans Araka and Lewis Mwalimu. The barber’s name was David Chege.

Evans Araka was a credit manager at Islamic Relief. His fiancée, a Nigerian named Rebecca, posted on social media that the couple, who had five children together, had been due to marry in November.

Relatives of one victim, lorry driver David Muchoki Munene, had expressed concerns about his safety. His mother said she had asked him to leave his job and move closer home, but he refused.

Al-Shabaab has been at war with Kenya ever since Kenyan troops entered Somalia in 2011 to defeat them. According to the BBC, Muslims in northern Kenya increasingly see the group’s attacks on civilians and security forces as a threat to their own interests, and are making efforts to improve relations with the Christians working there.