NAIROBI, Kenya — A Kenyan security official says dozens of foreign fighters have defected from the al-Qaida-linked militant group in Somalia due to internal disputes, and many of those men have moved into Kenya

Al-Shabab and other militants are under increased scrutiny in Kenya following the Sept. 21 grenade-and-gunfire attack on Nairobi's Westgate Mall, an attack that killed at least 67 people.

The trial of four suspects arrested in conjunction with the mall attack opened in a Nairobi court on Wednesday. Two prosecution witnesses described how the mall came under attack by four gunmen.

A senior police official who insisted on anonymity to share internal information said Kenyan security officials are observing movements both into and out of Somalia by people suspected of being part of al-Shabab.