Gunmen have killed six people and abducted three others in the latest attack in the north-eastern border region with Somalia, police say. A local police chief told the BBC that Somali militants were to blame for the raid in Wajir district, in which two local officials were seized. There have been several attacks since Nairobi sent troops into Somalia to fight the al-Shabab Islamist group. No-one has claimed responsibility for the latest attack. North-Eastern Province police head Leo Nyongesa would not confirm to the BBC if any police officers were killed - despite earlier reports that at least three had died. He said two government administrative officials - the district officer and the registrar of persons - were among the three people seized in Wednesday night's raid. Mr Nyongesa told the BBC the Kenyan authorities believed members of the al-Qaeda linked al-Shabab group were responsible. He added that the attackers threw explosives and shot their way into the police post in the small town of Gerille, approximately 200km (125 miles) north of the Dadaab refugee camp, which is close to the scene of previous attacks. The latest attack comes as Human Rights Watch warns that Kenyan security forces were "beating and and arbitrarily detaining citizens and Somali refugees" in the Kenya-Somalia border area. Kenyan army spokesman Major Emmanuel Chirchir told HRW that he did not have knowledge of any abuses, but the military would investigate the claims. In October, Kenya sent troops into Somalia to pursue al-Shabab, blaming it for a wave of abductions. The militant group has denied involvement in raids on Kenya's coast last year, which targeted foreign tourists and threatened a valuable industry for the country. It said the Kenyan incursion was an act of war and it would take revenge. There have been a series of explosions targeting police officers since October. In December, two explosions near Dadaab killed at least two police officers and wounded several others. After two decades of violence of Somalia, al-Shabab controls many southern and central areas of the country. But Kenyan forces have pushed it back from the south, while Ethiopia and local militias have also gained ground in the west.