A Kenyan man has pleaded guilty to one of two grenade attacks in Nairobi this week and attested in court that he is a member of the Somali-based militant group al-Shabab.

Elgiva Bwire Oliacha pleaded guilty Wednesday to causing grievous bodily harm and other charges in connection with a grenade attack at a crowded bus stop Monday evening. The attack killed one person and wounded eight others.

Earlier Monday, another grenade attack at a Nairobi bar wounded at least 13 people. Authorities have not said who may have carried out the bar attack.

Police said they detained Oliacha late Tuesday, along with a weapons stockpile that included 13 hand grenades, two submachine guns and four pistols.

Al-Shabab has warned it will carry out attacks inside Kenya in response to the Kenyan army's incursion into southern Somalia.

Kenya blames the al-Qaida-linked group for a series of recent cross-border kidnappings of several foreigners, a claim al-Shabab denies.

Since entering Somalia ten days ago, Kenyan forces have carried out airstrikes and advanced close to al-Shabab-controlled towns but have yet to fight a major ground battle with the militant group.

Al-Shabab is fighting to topple the U.N.-backed Somali government and set up an Islamic state in Somalia. The group has lost ground to Somali government and African Union troops in recent months but still controls considerable territory in southern and central Somalia.