The head of the International Committee of the Red Cross on Thursday warned of a "crisis of hope" in Gaza, calling the humanitarian situation in the Palestinian enclave "dire".

At the end of a three-day trip to Israel and the Palestinian territories, Peter Maurer said conditions in Gaza were worsening by the day, with the two million residents getting only three or four hours of mains electricity a day.

Maurer said the power shortage had led to a water and sewage crisis, which in turn is having serious effects on the health system.

"While we can always argue on who did take what decision for what reason, the humanitarian consequences for the people of Gaza are dire and are really unacceptable," he said in English at a press conference in Jerusalem.

He said a "crisis of hope" in Gaza, and among Palestinians generally, was "the most lasting impression that I take away" from the trip.

During his visit, Maurer met with the Gaza head of Hamas, the Islamist movement that runs the strip, as well as Israeli Prime Minister Benjamin Netanyahu and Palestinian president Mahmud Abbas.

Israel has maintained a crippling blockade on Gaza for the past decade, while Egypt has also closed off its border in recent years, both citing security concerns.

Already dire humanitarian circumstances have been exacerbated in recent months by Abbas's Palestinian Authority seeking to squeeze Hamas, reducing the amount it pays for electricity to be piped to Gaza among other measures.

Hamas has fought three wars with Israel since 2008.

The Islamist movement is believed to retain the bodies of two soldiers killed in the 2014 war, as well as hold captive at least two Israeli civilians. Hamas has not publicly confirmed or denied the claims.

Netanyahu on Wednesday called for the ICRC to help return the prisoners and the soldiers's remains.

Maurer said he had discussed the return of both with Hamas, and reiterated the ICRC's position that not informing family members about the fate and location of their loved ones is a breach of international law.

But he did not visit the Israeli prisoners.