Sierra Leone's leader told 850 soldiers on the eve of their deployment as part of an African Union mission to war-torn Somalia on Tuesday that they were on "a great journey of peace".

President Ernest Koroma addressed the men as they took a break from intensive training in Freetown ahead of joining the AU Mission in Somalia (AMISOM), which is supporting government troops fighting the Al Qaeda-linked Shebab rebels.

He told the soldiers they were "on the brink (of embarking) on a great journey of peace, a journey of charitable gallantry, a journey to showcase how a transformed nation and its transformed military could be a force for democracy, peace and reconciliation".

"You have an overwhelming superiority in logistics, organisation and global goodwill with the hopes and prayers of Sierra Leoneans everywhere," he said in the televised speech.

Sierra Leone, recovering after the end of its civil war in 2002, has expressed a wish to assist in bringing peace to other countries and will deploy the battalion to Somalian capital Mogadishu in early April, the Sierra Leone Television channel said.

Despite a string of losses in recent months, the Shebab remain a potent threat in Somalia, still controlling rural areas as well as carrying out guerrilla attacks in areas apparently under government control.

Ethiopian troops, the strongest military power fighting the insurgents in Somalia's southwest since their November 2011 invasion, pulled out of the town of Hudur earlier this month, the capital of Bakool region.

Security sources say the withdrawal from Hudur could signal a wider pullout of Ethiopian forces including from the key city of Baidoa, warning that if this happens, the 17,000-strong AMISOM would be hugely overstretched.