Israeli air strikes on schools, homes and media offices are deeply concerning, Downing Street said, as fighting continued in the Middle East.
Downing Street said it was seeking answers from Israel about attacks that destroyed the building housing the Associated Press and other media organisations in Gaza.
But Boris Johnson’s official spokesman also expressed concern about Hamas using human shields to cover its operations.
Israeli forces launched one of the heaviest assaults of the campaign overnight.
A wave of heavy airstrikes on the Gaza Strip, resulted in Israel saying it destroyed nine miles of militant tunnels and the homes of nine alleged Hamas commanders.
Attacks over the weekend resulted in the destruction of an office building that housed media outlets including the Associated Press and Al Jazeera.
In Westminster the prime minister’s official spokesman said: “We are deeply concerned by UN reports that more than 23 schools and 500 homes as well as medical facilities and media offices have been destroyed or seriously damaged in Gaza.
“Israel has a legitimate right to defend its citizens from attack but in doing so it must make every effort to avoid civilian casualties and military action must be proportionate and in line with international humanitarian law.
“We are also concerned by reports that Hamas is again using civilian infrastructure and populations as cover for its operations.”
On the destruction of the AP and Al Jazeera offices, the spokesman added: “We are in contact with our US and European counterparts and urgently seeking more information from the Israeli government on this.”
Fighting began a week ago when Hamas fired long-range rockets at Jerusalem after weeks of clashes in the Holy City between Palestinian protesters and Israeli police.
Israel responded with air strikes and the pattern has kept up in the worst violence seen in the region since 2014.
The Campaign Against Arms Trade (CAAT) called for the UK Government to investigate if British-made weapons had been used in the bombardment of Gaza.
CAAT spokesman Andrew Smith said: “We know that UK-made arms have been used against Palestinians before, but that has done nothing to halt the flow of weapons.
“There must be a suspension of arms sales, and a full review into whether UK weapons have been used and if they are implicated in possible war crimes.”