(Adds detail, background)
NAIROBI, Sept 26 (Reuters) - Somali Islamist militants, who said they were behind a weekend assault on a Nairobi shopping mall, claimed responsibility on Thursday for an attack on a police post in Kenya's northeast region in which two officers were killed and another injured.
Twelve vehicles were also burned in Thursday's raid on an assistant county commissioner's office in Mandera, which the ministry blamed on "criminals", without elaborating further.
"Mujahideen forces last night raided a Kenyan police base in Mandera town, in the Muslim NE regions, killing 2 and injuring 3," the Somali group al Shabaab said on its Twitter account.
It said the "mujahideen", or fighters, burnt police vehicles and stole ammunition.
The attack followed a grenade blast late on Wednesday that killed one person in another northeastern town.
The two incidents come just days after Saturday's assault on a Nairobi shopping mall by al Qaeda-aligned al Shabaab militants that killed at least 72 people, including at least five of the attackers. Several foreigners were among the civilian victims.
The leader of al Shabaab, Ahmed Godane, also known as Mukhtar Abu al-Zubayrhas, confirmed his group was behind the mall attack, and warned of more strikes. He said the raid was in retaliation for Kenyan troops' incursion in October 2011 into southern Somalia to crush the insurgents.
Al Shabaab has carried out sporadic attacks in the northeast border region. The area is also prone to banditry and low-key clan clashes by pastoralist communities. (Reporting by Duncan Miriri and Edmund Blair; Editing by James Macharia and Alison Williams)