In Bibles based on the Hebrew Masoretic, this verse says that when King NebuChadnezzar heard that Egypt had sent an army to assist Judah, he temporarily lifted the siege.
However, the Greek Septuagint version of this verse indicates that upon hearing the news, NubuChadnezzar attacked.
So which source text is correct?
Historically, both are correct. A reader comments:
‘So, there was a short interruption of this siege when the Babylonians (Chaldeans) withdrew in order to drive back the Egyptians to whom King Zedekiah had appealed for help. But, after having taken care of this Egyptian threat, the Babylonians returned and resumed the siege, just as the prophet Jeremiah forewarned that they would do.’
In other words, they did attack, but it was after a brief withdrawal.
So which text is the original, and which is a later corruption? It is impossible to say.