Kenyan police have arrested 29 Ugandans suspected of seeking to join Islamist rebels in Somalia, a police spokesman said on Sunday.

The suspects were arrested in Nairobi and were "undergoing interrogation," Eric Kiraithe told AFP. "Police are investigating them because they are believed to have been headed to Somalia to fight" alongside Shebab rebels.

The 27 men and two women were arrested Friday in a Nairobi suburb after raising suspicions among their neighbours.

Recruitment by Somalia's Shebab rebels of young people across East Africa, notably in Kenya, Uganda and Tanzania, has been a source of growing concern for regional security services.

The United Nations warned last July that the Shebab was recruiting, raising money and even conducting training in Kenya, where networks linked to the Somali rebels were growing in strength.

The group warned of the danger of "a new generation of East African jihadists" including some recent converts to Islam and others attracted mainly by promises of money from the Islamist recruiters.

Many Kenyans are among detainees held by Ugandan authorities on suspicion of involvement in twin bomb attacks in Kampala in July 2010 that claimed 76 lives.

The Shebab, fighting Somalia's weak transition government backed by the international community, claimed responsibility for the attacks.

The Shebab have in recent months seen their grip on the centre and south of Somalia weakened by a Kenyan army offensive that began in mid-October, followed by an Ethiopian incursion in November.

The Shebab have since claimed responsibility for several reprisal attacks in northeastern Kenya.