JERUSALEM (AP) — The United Nations on Tuesday criticized Israel's closure of its only cargo crossing with the Gaza Strip, warning that the measure could have negative consequences.

In a statement, U.N. Special Coordinator Nickolay Mladenov urged Israel to reverse its decision.

Israel said it was closing the Kerem Shalom crossing on Monday to everything except essential humanitarian supplies in response to the incendiary kites and balloons that have been flown from Gaza into Israel over the last few months.

Israel and Egypt have maintained a blockade on Gaza for over a decade in an attempt to weaken Hamas, a militant group that seeks Israel's destruction. The blockade has caused widespread economic hardship.

Mladenov said he was "concerned about the consequences" of Israel's latest closure. "Humanitarian assistance is not a substitute for commerce and trade," he said.

He also urged Gaza's militant Hamas rulers to "do their part by maintaining calm, stopping incendiary kites and preventing other provocations."

The flaming kites, which have torched wide swaths of Israeli farmland, have come amid near-weekly demonstrations led by Hamas along the volatile frontier since late March. The demonstrations have been fueled in large part by widespread despair caused by the blockade, which has resulted in chronic electricity outages and unemployment approaching 50 percent.

Over 130 Palestinians have been killed by Israeli fire, drawing international criticism of Israel. Israel says demonstrators have tried to infiltrate into Israel to attack soldiers or civilians. It says it is defending a sovereign border and accuses Hamas of using the crowds as human shields.

On Tuesday, the military said it stopped a Palestinian boat that attempted to break the naval blockade, which limits Palestinians from sailing beyond six nautical miles off the Gazan coast. It was the second attempt made in the past two months to breach the blockade.

The boat carried 10 passengers, seven of whom were medical patients. The military said it assigned medical staff to treat the patients who were on board.

The Israeli military defended its naval blockade, calling it "a necessary and legal security measure" to protect its citizens "in the face of terror and smuggling weapons."