Police officials in Kenya said Saturday that militants from the al-Shabab jihadist group hijacked a bus in the country and killed 28 people on board, who were non-Muslims. The bus was reportedly travelling to the capital city of Nairobi from Mandera town, when it was attacked about 31 miles from its point of origin on Saturday, the Associated Press reported.

Police officials said that the gunmen sorted the 60 passengers on board the bus and singled out non-Muslims before shooting them dead, AP reported.  The attack happened early Saturday and the Kenyan Inspector general said that the police would hold a press conference on the incident at 7:00 a.m. GMT (2:00 a.m. EST)

The al-Shabab group, whose name means “Youth,” is based in Somalia and is a part of the now defunct group Union of the Islamic Courts, according to a BBC report. The group, which is estimated to have nearly 9,000 fighters, has been banned by both the U.S. and the U.K. and has reportedly conducted at least 135 attacks since last September, when it attacked a shopping mall.

Al-Shabab, which claims to be allied with al Qaeda, has conducted various attacks in the Somali capital Mogadishu since 2006, and currently has control over large parts of the country. 

Last year, the group attacked the Westgate Shopping Mall in Nairobi, killing 67 people and injuring over 175. The attack was said to be retaliation for the Kenyan military’s incursion into Somalia in 2011, after several cross-border attacks were conducted by the group against aid workers and tourists.

In September, three German nationals, suspected of being affiliated with the al-Shabab group, were arrested at Frankfurt airport returning from Kenya. Earlier in the month, the U.S. announced that its military forces had conducted an operation against the group in Somalia, after it attacked the Somali intelligence headquarters and killed 10 people.