Angry demonstrations have been held at Erez, the main crossing point into the Gaza Strip from Israel.
Aid workers are protesting at being denied entry, saying the situation for the 1.5 million Palestinians living in Gaza under the tightening Israeli blockade is becoming untenable.
On Tuesday Israel resealed its border crossings with the Gaza Strip, blaming continuing rocket fire from Palestinian militants.
During talks on Monday Israeli Prime Minister Ehud Olmert told Palestinian President Mahmoud Abbas that he would not allow a humanitarian crisis to develop.
Abbas has urged Israel to abide by the terms of a five-month-old Egyptian-brokered truce with Hamas, which controls Gaza. The agreement has come under serious strain in recent weeks.
The UN High Commissioner for Human Rights, Navi Pillay, has said Israel’s blockade of Gaza deprives Palestinians of “the most basic human rights” and should end immediately.
Some 30 trucks laden with humanitarian aid were allowed in on Monday, but officials say the supplies will run out within days.