Declaration about leave in US government agency (5,10)
I believe the answer is:
state department
'government agency' is the definition.
(I've seen this before)
'declaration about leave in us' is the wordplay.
'declaration' becomes 'statement' (I've seen this before).
'about' is an insertion indicator.
'leave in us' becomes 'depart' (I am not sure about this - if you are sure you should believe this answer much more).
'statement' going around 'depart' is 'STATE DEPARTMENT'.
Can you help me to learn more?
(Other definitions for state department that I've seen before include "Washington office" , "US officials" , "government agency abroad" , "American diplomats" , "US Foreign Office" .)