I received the following question:

In Lamentations 3, is Jeremiah praying this destruction against fellow Israelite enemies, or against enemies of Babylon who took them into captivity?

I think the key here is found in verses 52-53, which read:

52. My enemies without cause
Hunted me down like a bird.
53. They silenced my life in the pit
And threw stones at me.

This casting of Jeremiah into a pit is described in Jeremiah 38:6.

6. So they took Jeremiah and cast him into the dungeon of Malchiah the king’s son, which was in the court of the prison, and they let Jeremiah down with ropes. And in the dungeon there was no water, but mire. So Jeremiah sank in the mire.

Who the “they” were who cast him there is described in verse 1 of chapter 38.

1. Now Shephatiah the son of Mattan, Gedaliah the son of Pashhur, Jucal the son of Shelemiah, and Pashhur the son of Malchiah heard the words that Jeremiah had spoken to all the people, saying,

So these men, called the “princes” in verse 4, are the enemies Jeremiah is speaking of later in this chapter when he says,

64. Repay them, O LORD,
According to the work of their hands.
65. Give them a veiled heart;
Your curse be upon them!
66. In Your anger,
Pursue and destroy them
From under the heavens of the LORD.

So it is indeed Israelite princes whom Jeremiah is praying against here.