Could I use clarify to calculate the first difference of a xtreg model?

[joufeihuang]

Dear Sir/Madam,

Hello, I am working on a xtreg model, while both my DV and IV are continuous variables. I have an interactive term (polity IV* Lagged by 1 year GDP growth). I use a country-year dataset.
My DV is the military expenditure (% GDP), IV is polity IV.
This is my Stata code:
estsimp xtreg military l.military c.polity##c.lagGDPgrowth lngdppc,fe
It reports that -estsimp- does not support the xtreg model
I went over the clarify pdf, does this package suitable for xtreg model?
Thank you so much!

Jou Fei