The United States placed the blame for the swift collapse of the latest Gaza ceasefire squarely at the door of Hamas on Friday, accusing the Palestinian militants of launching a "barbaric" attack.
President Barack Obama stressed it would be "very hard" to get another truce in the Gaza Strip unless Hamas showed it was serious about laying down its arms and could be trusted to keep its word.
Obama said the United States "unequivocally condemned Hamas and the Palestinian factions that were responsible for killing two Israeli soldiers, and abducting a third almost minutes after a ceasefire had been announced."
The US has staunchly stood by Israel's right to defend itself against Hamas rocket fire, but in recent days has been expressing mounting concern about the rising Palestinian civilian death toll in Israel's assault on Gaza.
US officials even went so far as to condemn the shelling of a UN school on Wednesday which left 16 Palestinians dead, saying there was little doubt that Israeli fire was at fault.
But on Friday, after reports that Hamas fighters had killed two Israeli soldiers and captured a third, the White House came down strongly on the side of Israel and demanded the soldier be released.
"If they are serious about trying to trying to resolve this situation, that soldier needs to be unconditionally released, as soon as possible," Obama told a surprise press conference.
"I think it's going to be very hard to put a ceasefire back together again if Israelis and the international community can't feel confident that Hamas can follow through on a ceasefire commitment."
But Obama also insisted that the deaths of "innocent civilians in Gaza caught in the crossfire have to weigh on our conscience and we have to do more to protect them."
Secretary of State John Kerry, who has spent days trying to negotiate a ceasefire, called Israeli Prime Minister Benjamin Netanyahu from India to discuss steps toward restoring calm, and said he would consult "regional partners" and the United Nations.
He denounced what he called an "outrageous violation of the ceasefire."
Signup to our newsletter and follow us on Facebook and Twitter!
Israel ended the three-day truce only hours after it began, accusing Hamas of ambushing its troops.
Hamas for its part accused Israel of breaching the ceasefire after intensive shelling killed dozens of people in southern Gaza.
- Hamas 'targets civilians' -
While it remains unclear exactly who has captured the Israeli soldier, White House spokesman Josh Earnest told CNN: "Apparently, Hamas individuals used the cover of a humanitarian ceasefire to attack Israeli soldiers and even to take one hostage. That would be a rather barbaric violation of the ceasefire."
And Obama said it was "not particularly revelant" whether Hamas or another group was behind the reported kidnapping of the Israeli soldier.
"The point is, when they sign on to a ceasefire, they're claiming to speak for all the Palestinian factions," he said.
Earlier, Gaza had enjoyed a brief respite after Kerry and the United Nations announced a "humanitarian truce," which should have been the longest of several agreed since the conflict broke out on July 8.
The fighting has killed nearly 1,500 on the Palestinian side, mostly civilians, and 63 Israeli soldiers and three civilians on the other.
US officials also defended Israel against charges that its assault on Gaza has been needlessly reckless with civilian lives.
"Hamas intentionally targets civilians. The Israelis do everything they can to avoid targeting civilians," deputy US national security advisor Tony Blinken told MSNBC television, accusing Hamas of using Palestinians as "in effect human shields."
"Israel holds itself to a very high standard, but what we've seen is that it's incredibly difficult to meet its very own high standard."