Seemingly Unrelated Negative Binomial (SUNB) estimation

Dear all,
I am trying to estimate a system of equations with a Seemingly Unrelated
Regression. However because of the characteristics of the data I'd like to
do it with a negative binomial estimation. Would anybody know how to
implement a Seemingly Unrelated Negative Binomial (SUNB) estimation in R?
Thank you in advance for your help.
Best regards,
Elisa Lanzi

Elisa Lanzi
PhD student in Economics and Organisation
School of Advanced Studies in Venice (SSAV)
email: elisa.lanzi at unive.it
website: http://venus.unive.it/elisa.lanzi