The United Nations criticized Israel for its ban on humanitarian aid entering the Gaza Strip in hearings that began on Monday in the International Court of Justice, the U.N.’s highest court. Israel, which did not send a legal delegation to the hearings, rejected the proceedings as biased.

For more than a month and a half, Israel has blocked food, medicine and other relief from entering the devastated Gaza Strip in an attempt to pressure Hamas to free the dozens of remaining Israeli hostages there. It argues that its blockade is lawful and that Gaza has enough provisions despite the restrictions.

The United Nations and aid groups say the blockade has further harmed Palestinians already reeling from more than a year and a half of war in Gaza, which has killed tens of thousands of people, displaced well over a million and leveled large swaths of the enclave’s cities.

During the two-month cease-fire that began in early January, aid had begun to flow into Gaza, providing a modicum of relief. But the blockade — which began in early March — continued after the truce ended with an Israeli bombardment and widening ground assaults against Hamas.

“No humanitarian aid or commercial goods have been allowed into Gaza since 2nd of March, which has devastating humanitarian consequences in the Gaza Strip,” Elinor Hammarskjöld, the U.N.’s top lawyer, told the court on the first day of five days of hearings.

The U.N. General Assembly requested in December that the International Court of Justice, also known as the World Court, issue an advisory opinion on Israel’s obligations to allow the United Nations and other third parties to provide humanitarian assistance for Palestinians. Some 40 governments are expected to speak during the hearings. An opinion is not expected for some time.