(Adds details on Israeli offensive, paragraphs 11-12)
JERUSALEM, Jan 17 (Reuters) - U.N. officials have said war crimes may have been committed during Israel's offensive in the Gaza Strip -- a suggestion Israeli officials reject out of hand.
"These claims of war crimes are not supported by the slightest piece of evidence," Yigal Palmor, an Israeli Foreign Ministry spokesman, said when asked if there was any chance of a case being brought to the International Criminal Court.
U.N. officials expressed outrage after Israeli tank fire killed two boys in a U.N. school on Saturday. John Ging, the head of the U.N. Relief and Works Agency (UNRWA) in Gaza, said he was concerned about possible war crimes.
"These two little boys are as innocent, indisputably, as they are dead," Ging told Reuters as Israel's offensive entered its 4th week. "The question now being asked is: is this and the killing of all other innocent civilians in Gaza a war crime?"
U.N. High Commissioner for Human Rights Navi Pillay called for independent investigations into possible war crimes after Israel's shelling of another U.N. school compound killed 42 people, including women and children, on Jan. 6.
Israel says the area near the compound was being used by militants to fire rockets.
The sheer number of Palestinian dead in the conflict -- 1,200, of whom 410 are children -- has also led to calls by human rights groups and aid workers for Israel to face examination under international criminal law, specifically on the issue of "proportionality" in the prosecution of the war.
Palmor said Israel's army had nothing to answer for.
"The army has a legal department that advises it and gives its opinion on measures that are taken," he said.
"As far as we know, the army has not done anything that is contrary to international law. Everything it did was according to international law and within international standards."
Yet Israeli army commanders admit they have seldom carried out such a full-throttle assault on an enemy.
"We've used artillery shells, tanks and helicopters for close-range assistance. I don't remember when we ever fired mortars in Gaza before," a battalion commander told Haaretz newspaper, which described Israel as acting like a steamroller.
BOTH SIDES IN VIOLATION?
A Palestinian rights group on Wednesday urged the International Criminal Court to investigate Israel, producing a 25-page petition alleging that Israel was using "terrorist weapons to conduct crimes against humanity".
The ICC prosecutor in the Hague responded by saying the court had no jurisdiction to investigate in Gaza. The ICC can investigate war crimes, crimes against humanity and genocide committed on the territory of, or by a national of, a state.
But Gaza is not a state. "In Gaza at present, the ICC lacks such jurisdiction," the prosecutor said in a statement.
While Israel has not signed the Rome Statute that enshrined the ICC, it can still be investigated, but it would require the U.N. Security Council to call for such a move. Any such proposal would likely draw a veto from Israel's ally, the United States.
"If you look at the ICC and the cases it has taken, whether it's the Congo, or Uganda, or potentially Sudan, they are looking at mass genocide or actions against children that are unprovoked or grotesque," said Jonathan Drimmer, an expert in war crimes issues at Steptoe & Johnson, a U.S. law firm.
"I think it's unlikely that it has legs to go to the International Criminal Court... That's not to excuse completely Israel's conduct, but it is to say that you do have complicating factors in assessing possible prosecutions that don't exist in other cases that the ICC has taken," he told Reuters.
Experts do believe, however, that both Israel and Hamas may have cases to answer on issues of humanitarian law.
Anthony Dworkin, the executive director of the Crimes of War Project and an expert in international humanitarian law, said Israel's broad approach to what it considered a target in the conflict might expose it to claims under the 1949 Geneva Conventions governing non-international conflict.
"Israel's thinking, evidently, is that all members of Hamas, and any facilities used to enforce their physical or ideological control over Gaza, are fair game," he wrote on his website, www.crimesofwar.org.
"Under the laws of war, such an approach is highly questionable." Referring to the targets hit he added: "It is hard to see how all these targets could be justified according to the rules of international humanitarian law."
At the same time, he said there was evidence Hamas's rocket fire into Israel was in violation of international law, and that the group may have used "human shields" to carry out attacks.
"In general," he wrote, "there appears to be a strong argument that both Israel and Hamas have violated international law in the conduct of hostilities in Gaza, by attacking people who are not themselves participating in hostilities." (Editing by Alistair Lyon)
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