"Agreed" or "agreed to"

In the second sentence, "The ... countries agreed to the ... package ..." is complete. There is a noun, the verb, and the predicate completely describes how the verb and noun relate. This sentence is correct.

In the first sentence, "The ... countries agreed the ... package ..." is incomplete. What did they agree or agree on? The package was good? The package was bad? They accepted the package? This sentence's predicate does not tell anything about the subject. This sentence is technically incorrect.

(If the sentence only said "The countries agreed," it would be complete and correct but it would not mean what the original sentence intended it to mean.)

"Agreed to that" is correct in this case.

The first seems ungrammatical to me. I speak US English, but I'm usually pretty familiar with UK English. At a minimum, it's a garden path sentence because it appears to be missing a predicate. For example, I'm fine with "The member countries agreed the bailout package for the sovereign was a good idea."

The OED has citations for transitive ‘agree’, in the sense ‘to arrange, concert, or settle (a thing in which various interests are concerned)’ from the sixteenth century onwards. In contemporary usage, there may be a transatlantic difference, with AmEng generally following ‘agree’ with ‘on, ‘to’ or ‘with’ and BrEng being comfortable with a direct object.