* Deadly raid with possible POW preceded truce - Hamas
* U.S., U.N. focus criticism on Palestinian Islamists
* Netanyahu seen holding course rather than escalating
* Gaza officials: 1,653 Palestinians killed in offensive
By Nidal al-Mughrabi and Dan Williams
GAZA/JERUSALEM, Aug 2 (Reuters) - Hamas acknowledged responsibility on Saturday for a deadly Gaza Strip ambush in which an Israeli army officer may have been captured, but said the incident likely preceded and therefore had not violated a U.S.- and U.N.-sponsored truce.
The statement by Hamas's armed wing, the Qassam Brigades, appeared aimed at preempting any intensification of Israel's 25-day-old offensive in the Palestinian enclave and deflecting international blame for the collapse of Friday's ceasefire.
But in a signal the war could wind down, Israel's military said its objectives, chiefly the destruction of tunnels dug by Hamas for cross-border attacks, were close to being achieved.
Israel says Hamas gunmen and a suicide bomber stormed out of a tunnel to ambush its infantrymen in southern Rafah a 9.30 a.m. on Friday, one and a half hours after the halt to hostilities came into effect, killing two troops and hauling another, Lieutenant Hadar Goldin, away through the underground passage.
The incident triggered Israeli shelling of Rafah from the mid-morning that killed 150 Palestinians. By early afternoon, Israel declared an end to the truce - which was meant to have lasted 72 hours, allowing humanitarian relief to reach Gaza's 1.8 million Palestinians and for further de-escalation talks.
Washington accused Hamas of a "barbaric" breach of the deal mediated by Egypt with the involvement of Turkey, Qatar and U.S.-backed Palestinian President Mahmoud Abbas. The United Nations said it had not verified the flare-up's causes, but questioned Hamas's truce commitment and urged Goldin be freed.
Hamas said it did not know what had happened to the soldier but if he was captured, he probably died in Israeli hostilities that followed the ambush.
Citing an internal investigation complicated by inability to communicate with its gunmen in the Rafah area, Hamas's Qassam Brigades said on Saturday it believed that the ambush took place at 7 a.m. in response to advances by Israeli ground forces.
"We lost contact with the (Hamas) troops deployed in the ambush and assess that these troops were probably killed by enemy bombardment, including the soldier said to be missing - presuming that our troops took him prisoner during the clash," the Brigades said in a statement.
"The Qassam Brigades has no information as of this time about the missing soldier, his whereabouts, or the circumstances of his disappearance."
Quoting an unnamed military officer, Israel Radio also said Goldin's condition was not known. It said he was last seen next to the two troops killed by a Hamas suicide bomber - suggesting he may not have survived either and his captors held a corpse.
Israel, with U.S. backing, had said that during any truce its ground forces would continue hunting cross-border tunnels. More than 30 of these, and dozens of access shafts, have already been located and were being blown up, the Israeli military says.
"Our understanding is that our objectives, most importantly the destruction of the tunnels, are close to completion," a military spokesman, Lieutenant-Colonel Peter Lerner, said.
Israel had long voiced concern that Palestinian guerrillas would try to capture a soldier or civilian. In 2011, Israel released more than 1,000 Palestinian prisoners in exchange for Gilad Shalit, a soldier snatched by Hamas five years earlier.
Israel has in the past twice freed prisoners in exchange for the bodies of soldiers held by Lebanon's Hezbollah guerrillas.
Hamas, whose gunmen are dispersed for battle in Gaza's battered districts, often in isolated, dug-in positions, said the continued manoeuvring by Israeli troops was a provocation.
"We informed the mediators who participated in arranging the humanitarian ceasefire of our agreement to cease fire against Zionist cities and settlements and that we cannot operationally cease fire against troops inside the Gaza Strip that conduct operations and move continuously," the Qassam Brigades said.
"These enemy forces could easily come in contact with our deployed ambushes, which will lead to a clash."
Rafah residents said they had received recorded telephone warnings from Israel to stay indoors during a barrage that wreaked devastation. Medical officials on Saturday counted at least a dozen homes destroyed, with the families who lived there each losing between two and eight members killed.
"It was like an action movie - explosions everywhere, cars flying up in flames, people crushed under houses that were bombed," local man Bassim Abed told Reuters. "It was a miracle I escaped the area. It's another miracle I didn't die of fear."
Ashraf Goma, Palestinian lawmaker from Abbas's Fatah party said 50,000 people in villages to the east of the town had been displaced. He accused Israel of committing a war crime.
Israel launched a Gaza air and naval offensive on July 8 following a surge of cross-border rocket salvoes by Hamas and other Palestinian guerrillas, later escalating into ground incursions centred along the tunnel-riddled eastern frontier of the enclave but often pushing into residential areas.
Palestinian officials say 1,653 Gazans, mostly civilians, have been killed. Sixty-three Israeli soldiers have been killed, and Palestinian shelling has killed three civilians in Israel.
EYES ON EGYPT
Hamas said it launched long-range rockets on Saturday at the Israeli cities of Haifa and Tel Aviv. There was no word in Israel of Haifa being struck, but the military said its Iron Dome interceptor had shot down rockets over Tel Aviv and the southern city of Beersheba. No one was hurt by the salvo.
Among targets of Israeli air strikes on Saturday was a building in the Islamic University campus in Gaza City. The military said the building had been used by Hamas for weapons research and development of weapon manufacturing, and that dozens of tunnels and arms caches had been bombed elsewhere.
After Friday's ceasefire was shattered, Israeli Prime Minister Benjamin Netanyahu called his security cabinet into special session and warned Hamas and other militant groups they would "bear the consequences of their actions".
Israeli media quoted unnamed government officials as saying Netanyahu and Defence Minister Moshe Yaalon would hold course in Gaza - suggesting that rather than escalate, they would stick to a tunnel-hunt the military predicts could be over within days.
Egypt was due to host a Palestinian delegation later on Saturday to try to salvage the truce. Israeli envoys had also been expected in Cairo at the weekend, but Netanyahu government officials did not immediately say whether they would still go.
"The Egyptian initiative is a real chance to find a real solution to the crisis taking place in the Gaza Strip," President Abdel Fattah al-Sisi told reporters. "Lost time ... complicates the situation more and more."
Hamas is seeking an end to Israel's blockade of Gaza. It also wants a hostile Egypt to ease restrictions at its Rafah crossing with the territory.
In a boost to Israel, the U.S. Congress approved $225 million in emergency funding for Iron Dome. (Writing by Dan Williams; Additional reporting by Mostafa Hashem and Oliver Holmes in Cairo; Editing by Giles Elgood)