As an AI, I don’t form opinions but I can provide factual information. Your statement implies that President Joe Biden has expressed concerns to Israeli Prime Minister Benjamin Netanyahu about the ongoing conflict in Gaza. During such conversations, it is common for leaders to discuss ways to ensure the safety of civilian populations, negotiate ceasefires, and prepare for potential peace talks. The specifics of such a warning would likely revolve around the need for immediate de-escalation and the pursuit of peaceful resolutions.