More than 30 Kenya-based members of Somalia's top militant group have accepted a police amnesty and are providing information to help officers prevent threatened suicide attacks.
Police spokesman Eric Kiraithe said that some of the men are Kenyan citizens, while others are refugees from neighbouring Somalia, where the al Qaida-linked al-Shabab militant group is based.
"I can assure you a lot of young men from this country and also from Somalia are working with us now to secure this country, and we believe that basically internally al-Shabab is losing its foothold at a very fast rate," Mr Kiraithe said.
Kenyan troops last month moved into southern Somalia in pursuit of al-Shabab militants in response to a string of attacks and kidnappings in Kenya, including those of four European tourists. Al-Shabab threatened to retaliate with large-scale terror attacks in Nairobi, Kenya's capital.
Police blame al-Shabab for recent attacks that have killed seven people in Kenya in the past few weeks.
Kenyan police commissioner Mathew Iteere extended amnesty to Kenyans recruited by al-Shabab following twin grenade attacks on the capital late last month. A non-Somali Kenyan was convicted to life in prison for one of the grenade attacks at a city bus stop, which killed one person.
Elgiva Bwire Oliacha, 28, was sentenced to life in prison after he pleaded guilty to several charges, including being a member of al-Shabab.
A July UN report warned that al-Shabab was recruiting non-Somali members from countries in East Africa and was giving a rise to a new generation of East African jihadists. The groups represent a new security challenge for the region and wider international community, the report said.
The report, by a panel of UN experts monitoring arms embargoes against Somalia and Eritrea, said that in the past al-Shabab's presence in Kenya was concentrated primarily within the ethnic Somali community.
But since 2009 the group has rapidly expanded its influence and membership to non-Somali Kenyans who now make up the largest group of non-Somalis in al-Shabab.