In the final section of the oracle against Moab (Jeremiah 48:40–47), it is clearly stated that the Lord is speaking, Thus says the Lord.
The Lord begins the section with a description of one who will fly swiftly like an eagle and spread his wings against Moab.
A bird of prey swooping onto its prey is a well-known image in Scripture that describes the invasion of an enemy (Ezekiel 17:3–8). The point here is not to necessarily identify the enemy, but rather to describe how deadly the enemy is for Moab.1 The result will be that cities in Moab are taken, strongholds seized. The invasion will be so swift and ferocious that the warriors of Moab will be left paralyzed and vulnerable because of fear, like the heart of a woman in her birth pains.
40 For thus says the LORD: “Behold, one shall fly swiftly like an eagle and spread his wings against Moab;