Julie Bishop *troubled* by Gaza suffering (AAP)

AAP Foreign Minister Julie Bishop has said she is "deeply troubled" by Palestinian deaths in Gaza.

Australia is backing calls for a full investigation into Israel's "indefensible" shelling of three United Nations schools in Gaza where civilians were sheltering.

In her most strongly-worded statement yet Foreign Minister Julie Bishop said she was "deeply troubled" by the suffering and death endured by Palestinians in the nearly month-long conflict.

Israel had a right to defend itself but must take all necessary steps to prevent civilian casualties, she added.

Ms Bishop acknowledged that hundreds of innocent civilians had been killed in Gaza since the conflict began.

"There have been a number of shocking incidents, including the indefensible shelling of three UN schools, all of which were sheltering civilians," Ms Bishop said in a statement on Tuesday.

Her comments followed a similar condemnation from Israel's key ally the United States, which expressed its shock at the latest "disgraceful" shelling of the school.

It's the third time in 10 days a UN school has been hit in fighting that has claimed the lives of at least 1800 Palestinians and 65 Israelis in and around the Gaza Strip.

Ms Bishop said Australia would support calls for a full investigation into these incidents, declaring both Israel and Hamas must respect international humanitarian law.

The Abbott government has been criticised in some quarters - including reportedly by its own backbench - for not speaking out enough against Israel as the Palestinian death toll has mounted.

Labor blasted Israel's shelling of the UN schools as "appalling" and urged the government to use its position on the UN Security Council to push for an immediate ceasefire.

Both sides of politics condemned Hamas' use of civilian facilities to stockpile weapons and its indiscriminate missile attacks against Israel.

Ms Bishop said she hoped a 72-hour ceasefire to take effect on Tuesday would pave the way for a more lasting end to the cycle of "killing and recrimination" in the narrow coastal enclave.

http://au.news.yahoo.com/a/-/latest/24634872/julie-bishop-troubled-by-gaza-suffering/