Palestinian militants launched nearly 20 rockets at Israel on Friday hours after Israel began cutting electricity to the Gaza Strip in an attempt to halt the barrages.

Late Thursday, Israel cut back around one percent of the power it supplies to Gaza, Defense Minister spokesman Shlomo Dror said. Israel will continue gradually scaling back electricity until the territory's Hamas rulers end the rocket fire, he said Friday.

"It's their choice. They need to choose if they want to keep investing in rockets and in attacking Israel or if they want electricity from Israel," Dror said.

Hamas has said it will not be cowed by the sanctions.

One of the rockets damaged a factory in southern Israel Friday, according to police spokesman Micky Rosenfeld. There were no casualties, he said.

Israel moved into a new phase of sanctions with the power cut after earlier reducing fuel supplies to the beleaguered territory.

Human rights groups have complained that measures like cutting back on fuel and power are collective punishment, harming innocent civilians. Israel says the moves are more humane than large military operations aimed at halting the fire, which would cause scores of casualties, and insists it will not cause a humanitarian crisis in Gaza.

Gaza generates about a quarter of its own electricity at a plant run on fuel imported from Israel. The rest comes over 10 electricity lines directly from Israel and two from Egypt.

A fuel cutoff last month led Hamas to shut down the Gaza City power plant, causing blackouts in most of Gaza City and embarrassing Israel, which resumed some fuel shipments within days. Then Hamas knocked down much of the wall between Gaza and Egypt on Jan. 23, giving hundreds of thousands of Gazans a brief taste of freedom until Egypt closed the breaks 12 days later.

Hamas overran Gaza in June, expelling Fatah forces loyal to Palestinian President Mahmoud Abbas, who now runs a government in the West Bank.

Six Palestinian militants and one civilian were killed in Israeli operations against rocket squads in Gaza Thursday.