Pray Not For Them

Jeremiah is told not to pray for the people of Judah for they had made a great conspiracy against the Lord. Are there some sins unto death that the Lord says, pray not for them? This is a hard question yet it appears that that is just what Jeremiah was to avoid doing. What are we to do with the reprobate? What are we to do toward those that sin a sin unto death? What are we to do when some account that the work of the Spirit of God is the work of Satan? Prayer is always want to be made yet Jeremiahs is told not to pray in this occasion.