The Israeli military says its troops have taken “operational control” of the Palestinian side of the Rafah border crossing between Gaza and Egypt.
Rafah has been a key entry point for aid and the only exit for people able to flee since the start of the war between Israel and Hamas in October.
A tank brigade moved in to the crossing area after a night of intense strikes.
The UN warned that the closure of Rafah meant that the two main aid arteries for Gaza were currently “choked off”.
On Monday, the Israeli military ordered tens of thousands of civilians to begin evacuating nearby eastern parts of Rafah city ahead of what it called a “limited” operation.
Hamas said Israel’s seizure of the Rafah crossing was aimed at undermining attempts by regional mediators to secure a new ceasefire deal.
The Palestinian armed group announced on Monday that it had accepted a proposal from Egypt and Qatar, the basis of which is a weeks-long pause in the fighting and the release of several dozen hostages still held in Gaza.
