Israel has closed crossings into Gaza following a rocket attack on the Israeli town of Sderot by Palestinian fighters.
Monday’s closures were the first during this Ramadan, the Muslim holy month of fasting.
The rocket hit an open area in Sderot, starting a fire but causing no casualties.
The attack, the first in nearly three weeks, violates a June ceasefire agreement between Israel and Hamas, the Palestinian faction that rules Gaza.
No one claimed responsibility for the rocket fire.
Following the incident, Ehud Barak, the Israeli defence minister, ordered that the crossings be closed indefinitely.
The move effectively seals off the Gaza Strip which badly needs supplies for its 1.5 million Palestinians.
Hamas denounced the Israeli reaction as "sabotage" against the truce.