By Elizabeth Blunt
BBC News, Addis Ababa
Somali PM Ali Mohamed Ghedi has said the head of the World Food Programme in the country, who was arrested by troops on Thursday, is under investigation.
Mr Ghedi has been holding talks with the Ethiopian government
But Mr Ghedi did not say if any charges had been brought against Idris Osman.
The UN has protested strongly against Mr Osman's detention, but has said it has not yet received an explanation.
Mr Ghedi was speaking during a visit to Ethiopia, where he has been discussing both the rift in Somalia's transitional federal government and his own future.
It is no secret that Mr Ghedi has fallen out badly with Somalia's President, Abdullahi Yusuf Ahmed.
Mr Abdullahi says the prime minister's term of office has expired, but Mr Ghedi is unwilling to go and he is expected to fly home to Somalia on Saturday to face a vote of confidence in parliament.
After being summoned to Addis Ababa and spending two days in talks with members of the Ethiopian government, Mr Ghedi appeared at a news conference looking sombre and slightly shaken.
He denied that there was any personal animosity between himself and the president, saying that this was merely a procedural disagreement and one that would be solved by parliament according to the law.
While the prime minister has been in Ethiopia, a new crisis has erupted in Mogadishu, with the arrest at gunpoint of Mr Osman when the UN compound in Mogadishu was stormed by government security forces.
The UN compound in Mogadishu was stormed by security forces
The WFP subsequently stopped distributing food aid in Mogadishu in protest at the move, which UN Secretary General Ban Ki-moon condemned as "forceful and illegal".
When he was asked about the incident, Mr Ghedi was unapologetic.
"Mr Idris is under the custody of the national security forces, comfortably in a very clean and stable place, meeting with his family members," he said.
"If Mr Idris is innocent after a quick investigation, he will be released without conditions. If he is guilty, he will go to justice."
But what he refused to say, despite repeated questioning, was what the UN employee was suspected of committing.