pursuant: adverb or adjective

Here is the definition of “pursuant” in my dictionary:
pursuant
pursuant /pəˈsjuː.ənt/ US /pɚˈsuː-/
adjective [after verb] FORMAL OR LEGAL
according to:
The fact that a person acted pursuant to an order of his government does not relieve him from responsibility under international law.
I am curious to know why “pursuant” is classified as an adjective not an adverb in this case.
“pursuant” comes after a verb so I tend to think it is an adverb but this isn’t the case.

The adverb woud be ‘pursuantly’ . ‘Pursuant to’ is an adjectival phrase, similar to ‘in accordance with’.