NAIROBI, Kenya (AP) — Suspected Islamic extremists killed six people in an attack in northern Kenya near the border with Somalia, an official said Thursday, while the al-Shabab extremist group claimed it had targeted Christians.

The gunmen were targeting 33 non-Muslims living in a residential block but a quick response by security forces saved other lives, Mandera County Governor Ali Roba said in a statement. He said the attack occurred near the Bulla area in the early morning.

The Somalia-based Al-Shabab, through its Andulus radio station, claimed responsibility for the attack.

The station quoted an unnamed al-Shabab official saying: "It was a well-planned attack which targeted Christian members in Mandera ... We have eliminated the enemy members (who) were targeted."

Kenya has experienced a wave of attacks from al-Shabab, which is allied to al-Qaida. 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.

Both Mandera County and Garissa County, which border Somalia, have been targeted by al-Shabab. The worst attack was in April 2015, when al-Shabab gunmen killed 148, most of them students, at Garissa University.

Suspected al-Shabab gunmen killed at least six people when they shot at two buses traveling in Mandera County in July.

Al-Shabab extremists also hijacked a bus traveling through Mandera County in November 2014 and killed 28 non-Muslims on board. In December 2014, they killed 36 quarry workers in Mandera town.

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Associated Press writer Abdi Guled contributed to this report from Mogadishu, Somalia.