Immigration approval letter for work visa

I am a US citizen trying to arrange a work visa for Ethiopia. The Ethiopian embassy here in the USA requires a letter of approval from Ethiopian immigration before issuing a work visa. Unfortunately, I have been unable to determine exactly HOW one does this. The government does not make this clear.

My host in Ethiopia has no no idea how to do this. (This is small scientific research collaboration so nobody has any experience in this area). The embassy assures me that immigration approval is "instant" once host applies in Addis but has not provided details about HOW one does this.

Can anybody help? Can immigration approval letter be obtained online? Does somebody have to visit an office in Addis?

I have been unable to find info online. I have tried calling immigration office in Addis but calls never get through. This bureaucratic catch has held up project for several weeks and threatens to derail entire project. Can anybody offer any suggestions?

Thanks for any help.

I HAVE THE EXACT QUESTION ,   Let me know if you get an answer .. THANK YOU

Your host in Addis needs to approach the immigration office here with a letter explaining why and for how long you will be coming to the country along with a copy of your passport and a copy of a valid business license with atleast ETB 2 million (approx $100,000) as registered capital. It is possible if it is less but is possible if your contact can convince that you coming will benefit the country.
Once approved they will scan and send the application to the embassy that your contact requested on the letter.

The above answer is fine.. Another route if it is research would be to try and do it through AA university if the organisation has contacts there..ie get a research student visa rather than work permit.