US President Joe Biden has told Israeli Prime Minister Benjamin Netanyahu that the United States does not support ground operations in Rafah on the southern edge of Gaza.
Biden's comments came as Israeli forces instructed people to leave parts of eastern Rafah, warning of an imminent military operation.
Israel later said it was conducting limited operations in the city -- home to about 1.2 million people including many evacuees.
White House national security spokesperson John Kirby said Biden told Netanyahu during a phone call on Monday that the US does not support ground operations that would put any civilians at risk.
Kirby said, "We're asking questions of the Israelis about what their intentions are here, and what the larger purpose of this evacuation is."
Netanyahu's office said on Monday that his war cabinet unanimously approved continuing the military operation in Rafah, to exert pressure on Hamas and advance the release of hostages held in Gaza.
While attention is focused on a possible Israeli ground offensive, Hamas said in a statement on Monday that it has accepted a ceasefire proposal.
Kirby indicated that negotiations have reached a critical stage. He said: "We want to get these hostages out, we want to get a ceasefire in place for six weeks, increase humanitarian assistance. We still believe that reaching an agreement is the absolute best outcome."