The United Nations has warned that longer power cuts threaten a "total collapse" of basic services in Gaza, with residents in the beseiged Palestinian territory being held hostage to political infighting.
Gazans currently receive three to four hours of mains electricity a day, delivered from the territory's own power station and others in Israel and Egypt.
Israel decided on Sunday to reduce the amount of electricity it supplies to Gaza by between 45 and 60 minutes a day after Palestinian Authority President Mahmoud Abbas cut electricity funding by his West Bank-based Palestinian Authority.
The move was widely seen as an attempt by Abbas to step up pressure on the rival Hamas movement, which runs Gaza.
The UN humanitarian coordinator for the occupied territories, Robert Piper, warned the additional power cuts would have a disastrous effect.
"A further increase in the length of blackouts is likely to lead to a total collapse of basic services, including critical functions in the health, water and sanitation sectors," Piper said in a statement.
"The people in Gaza should not be held hostage to this long-standing internal Palestinian dispute," he said.
Israeli and global NGOs, including Amnesty International, joined the world body in condemning the longer hours of blackout.
A joint statement of 16 groups, among them Israel's B'Tselem, Peace Now and Rabbis for Human Rights, said they have asked Israel's attorney general to intervene.
They said further cuts would contravene a 2008 Israeli supreme court ruling that years of Israeli control over the strip had created near-total dependence on power supply from Israel and it must therefore continue to provide sufficient electricity to meet humanitarian needs.
Amnesty warned in a separate statement of a "looming humanitarian catastrophe".
It said additional reductions in power "will have a disastrous impact on Gaza's battered infrastructure and cause a public health disaster".
"The move will also endanger thousands of lives including those of hospital patients with chronic conditions or in intensive care, including babies on life support."
Israeli Prime Minister Benjamin Netanyahu said on Tuesday that Israel had "no interest in an escalation," blaming internal Palestinian disputes for the crisis.
Hamas said the cut was made on Abbas's orders and termed it "a catastrophe".
"This decision aggravates the situation and risks an explosion in the Gaza Strip," it said on Monday.
Hamas has run Gaza since 2007, when it seized the territory from Abbas's Fatah movement in a dispute over parliamentary elections won by Hamas the previous year.
Multiple attempts at reconciliation between Hamas and Abbas's Fatah movement have failed, but the Palestinian Authority has continued to pay Israel for some electricity delivered to Gaza.
The prospect of even lengthier blackouts in Gaza has raised fears of a new upsurge in violence.
Israel and Hamas have fought three wars since 2008.
Source: News agencies