The Kenyan military said on Sunday the deaths occurred during a dawn attack by the militant Islamist group on a military camp at Buare in the coastal region of Lamu, close to Somalia, where al-Shabab is based.
Military spokesman Colonel David Obonyo said that two unidentified Caucasian men were among the militants killed in the fighting.
The militant group recruits foreign fighters both from neigboring countries and abroad, including from the USA and Britain.
Al-Shabab has denied losing 11 fighters, and put the number of army fatalities at three. The group also claimed to have destroyed a military vehicle carrying Kenyan soldiers on Sunday in a separate attack near the border village of Haluqa in the county of Garissa.
The attack in Lamu comes as Kenya prepares to mark the anniversary of an al-Shabab raid in the town of Mpeketoni, also in Lamu, in which at least 48 non-Muslims were killed.
In April, the Islamists raided a university in the northern Kenyan city of Garissa, killing nearly 150 students.
Al-Shabab militants say they are carrying out attacks in neighboring Kenya in retaliation for its participation in an African Union peacekeeping force in Somalia that is fighting against their group.
The militants are seeking to topple the Western-backed Somali government and to impose their strict version of Islamic law in the country.
tj/ (AP, dpa, Reuters)