Albert Barnes Commentary 2 Kings 24:10

"At that time the servants of Nebuchadnezzar king of Babylon came up to Jerusalem, and the city was besieged." — 2 Kings 24:10 (ASV)

Came up against Jerusalem - The cause and circumstances of this siege are equally obscure. Perhaps Nebuchadnezzar detected Jehoiachin in some attempt to open communications with Egypt.