Israel said it was reducing electrical power to the Gaza Strip on Friday as part of its plan to sever economic ties with the territory.

The move was the latest in a series of Israeli steps that increases pressure on Gaza, ruled by the Islamist Hamas since last June and the source of repeated rocket attacks into the Jewish state.

Critics have accused Israel of imposing a blockade that amounts to "collective punishment" of the population of the territory after it cut fuel to Gaza's main power plant last month, leading to blackouts.

"We are trying to reduce the Gaza Strip's dependence on Israel in many fields ... the High Court ruled that we are acting in a correct and appropriate manner," deputy Defence Minister Matan Vilnai said.

A spokesman for Vilnai said Israel would reduce electricity on one of ten high-power lines by less than one megawatt by the end of Friday. It would eventually reduce power by some five percent of the 124 megawatts it supplies the Gaza Strip.

"This is not punishment ... we have disengaged from them by pulling out our troops and settlers and now we want them to start looking after themselves, they have their own power station, they get power from Egypt, we want them to ... stop relying on Israel," spokesman Eitan Ginsburg said.

Israel Radio reported on Thursday night that the power reduction had already begun.

Ginsburg said that apart from Israel's 124 megawatts, a local power station in Gaza City produced 64 megawatts and Egypt supplied 17 megawatts.

Asked to comment, U.S. State Dept spokesman Tom Casey said he was not familiar with the Israeli decision, but added: "We understand Israel's right to defend itself, but we do not think that actions should be taken that would infringe upon or worsen the humanitarian situation for the civilian population in Gaza."

The U.N. Human Rights Council said last month it deplored the "grave violations" being committed by Israel in Gaza and demanded it lift its blockade. The European Union has condemned the cordon as "collective punishment" on Gazans.

Israeli troops backed by tanks, helicopter gunships and warplanes killed six Palestinian gunmen and a schoolteacher in a raid in the Hamas-ruled Gaza Strip on Thursday, militant groups and hospital officials said.

Israel has stepped up military action against Hamas since it claimed responsibility for a Palestinian suicide bombing on Monday, the first such attack by the Islamist faction inside the Jewish state since 2004.

BORDER

Palestinian militants blasted open the territory's border with Egypt last month in defiance of an Israeli blockade. Egypt re-sealed the border on Sunday.

Last month Vilnai said Israel wanted to wash its hands of Gaza altogether by handing over the supply of electricity, water and medicine to others.

Israel declared Gaza an "enemy entity" last September, three months after Hamas routed the rival Fatah faction for control of the coastal enclave, whose eastern and southern borders, sea access and airspace are controlled by Israel.

The "enemy" designation was a green light for sanctions although Israel said it would not inflict a humanitarian crisis on Gaza's 1.5 million people.

Hamas has described militant attacks on Israel, which have also been condemned internationally, as responses to Israeli military operations in Gaza and the occupied West Bank.

Makeshift Palestinian rockets rarely cause deaths in Israel but have spread panic in its southern border towns.

On Thursday the Israeli army said troops had uncovered underground rocket silos in the northern Gaza Strip. Israel has threatened a major ground offensive into Gaza to try to end the rocket salvoes.