UN children organisation's Rozanne Chorlton said al-Shabab had given UN workers unhindered access and hoped this would encourage other agencies.

It comes as the UK pledged £52.25m (US$84m) in emergency drought aid.

But the UK's overseas aid minister said the UK would not deal with al-Shabab, which controls much of Somalia.

Andrew Mitchell is touring the huge Dadaab camp in north-eastern Kenya to see the scale of the crisis caused by the drought, the Horn of Africa's worst in 60 years which is estimated to be affecting some 10 million people.