Egypt, Israel, the United States and the United Nations were still negotiating over thorny issues, including who would inspect the shipments for weapons, officials said.
The fighting between Israel and Hamas has raised fears that the violence will spill into Lebanon as a wider conflict with Hezbollah. Such a war would be dangerous for all involved.
Another attack at a school, three years after the beheading of a teacher, has heightened anxiety about a new wave of terrorism in an already scarred country.
The administration has grown increasingly anxious that Israel’s enemies may seek to widen the war with Hamas and has both sent diplomatic messages and deployed military assets to prevent it.