JERUSALEM (CNN)  -- Israel reduced the flow of fuel to Hamas-controlled Gaza on Sunday, a move it vowed to take in response to "the incessant firing of rockets into Israel," an adviser to Prime Minister Ehud Olmert said.

Workers unload gas canisters Sunday at a factory in Gaza City.

Ten Israeli and Palestinian human rights groups are petitioning Israel's Supreme Court to stop the reduction.

The Israeli company Dor Alon supplies fuel to Gaza. Dor Alon had previously halted fuel shipments following Hamas' takeover of Gaza earlier this year, but restarted them.

It's unclear how the new reductions will affect Gaza's power plant, which is fueled by Dor Alon. The Israeli daily, Haaretz, reported the power plant received a full supply of fuel Sunday.

But Ahmed Ali, deputy director of Gaza's Petroleum Authority, told The Associated Press that fuel shipments on Sunday were more than 30 percent below normal.

He said Israel delivered 52,835 gallons of diesel fuel, compared to the typical 92,500 gallons on a normal day, and 23,775 gallons of gasoline, instead of the regular supply of 40,000 gallons. He said Gaza keeps about four days of fuel reserves, the AP reported.

Israeli Defense Minister Ehud Barak approved the fuel cuts Thursday as part of a plan by Israeli security officials looking to stem rocket attacks on southern Israel.

Olmert's government has been under mounting pressure to do something about the rocket attacks.

According to the Israel Defense Forces, about 800 rockets were fired into Israel from June to September, 60 percent more than were fired during the same period in 2006.

Some Israeli officials downplayed the significance of the reduction. Speaking on Israel Army Radio, Israeli Deputy Defense Minister Matan Vilnai said the plan would "gradually [cut] the electricity supply without harming humanitarian sources like hospitals."

And Israeli government spokeswoman Miri Eisin said Israel remains "committed that there will not be a humanitarian crisis" in Gaza as a result of its action

But the human rights groups petitioning Israel's Supreme Court said "the consequences of disrupting electricity and fuel supplies cannot be controlled or predicted." They are demanding the court "issue an immediate injunction to freeze the aforementioned governmental decision pending its hearing of the petition."

Last month, the Israeli Cabinet labeled Gaza a "hostile territory," a move quickly criticized by Palestinian Authority President Mahmoud Abbas, who said the designation would sabotage his government's efforts to extend its mandate into Gaza. The United Nations also criticized the decision.

"There should be no sanctions against the Palestinian people, neither individual nor collective punishment," Abbas said days after the Israeli Cabinet's decision. "It will harm our bilateral relations. It will harm our discussions and negotiations. It will harm the atmosphere and even sabotage it."

In June, Hamas seized control of the Palestinian territory of Gaza from forces loyal to Abbas' Fatah party. The Palestinian leadership split as a result, with Fatah leaders consolidating their power in the West Bank.

Abbas has aligned himself with the United States and the European Union, reopening access to millions of dollars in aid that had been frozen after Hamas won elections in January.

After the Israeli Cabinet's unanimous decision last month, Chris Gunness of U.N. Relief and Works Agency said the impact of the measures would be "extremely detrimental" to the humanitarian situation in Gaza.

"This would be just another tightening of the knot on Gaza," he said, adding that 1.2 million Gazans are already receiving emergency food rations.

Also, said Gunness, the Cabinet action will "further radicalize the youth," as more are forced into unemployment.

Israeli Foreign Ministry spokesman Mark Regev said Israel must respond to the barrage of attacks on Israel.

"We've had a situation where, day after day, week after week, month after month, we've had rockets fired from Gaza by extremists, designed to kill our people," Regev said. "The Israeli cabinet has decided that this situation just can't go on and we will act to defend our citizens."