US cautions Israel on civilian casualties as ground invasion continues.

US cautions Israel on civilian casualties as ground invasion continues

White House calls on Israel to restrict itself to 'precise operation' in Gaza while stressing its right to defend itself

Israeli troops and tanks are engaged in fierce fighting in Gaza following the launch of a military ground operation on Thursday night with the initial aim of eliminating Hamas tunnels that could be used to launch attacks on Israel.

Hamas warned Israel of the "dreadful consequences" of the conflict's escalation, while the US urged its close ally to restrict itself to a "precise" operation.

In a night of sustained bombardment as well ground fighting, Israel suffered its first military casualty of the 11-day war. The dead soldier – named as Eitan Barak, 20 – was possibly killed by so-called friendly fire in the north of Gaza. Two others were injured.

The Palestinian death toll since the start of the conflict exceeded 250, including at least 11 who were killed overnight. Israel launched air strikes against more than 100 targets overnight.

The Israeli prime minister, Binyamin Netanyahu, and the defence minister, Moshe Ya'alon, instructed the army to be prepared to expand the ground operation. The mobilisation of a further 18,000 reservists was authorised overnight, bringing the total on standby to about 60,000 in addition to those in service.

Netanyahu was due to make a statement on the escalation of the military operation on Friday morning, and his inner security cabinet was convening.

"In light of Hamas's incessant criminal aggression and dangerous infiltration into Israeli territory, Israel must act to protect its citizens," a statement from the prime minister's office said.

"Operation Protective Edge will continue until it has achieved its purpose – restoring quiet to the citizens of Israel for an extended period, with significant damage to the infrastructure of Hamas and other terrorist organisations in the Gaza Strip."

IDF spokesman Brig Gen Moti Almoz said: "We are now entering the second part of the operation. We delivered a hard blow to Hamas: We attacked thousands of targets, destroyed infrastructure, hurt operatives. Large ground troops are taking over targets in the Gaza Strip, operating against tunnels and infrastructure."

The US called on Israel to restrict itself to a "precise operation" on the ground in Gaza while stressing its right to defend itself against rocket attacks.

In a statement late on Thursday, the state department said Netanyahu had telephoned the US secretary of state, John Kerry, to explain his decision "to launch an operation to target the threat of further terrorist infiltration through tunnels into Israel".

It continued: "The secretary reaffirmed our strong support for Israel's right to defend itself against terrorist threats emanating from tunnels into Israel and expressed our view that this should be a precise operation to target tunnels, as described in a statement from the Israel Defence Forces."

It said Kerry emphasised the need to "avoid further escalation and to restore the 2012 ceasefire as soon as possible".

Hamas responded to the invasion with characteristic rhetoric. "We warn Netanyahu of the dreadful consequences of such a foolish act," Hamas official Sami Abu Zuhri told Reuters.

A statement issued by Hamas warned Israel: "We're with you in the field, and we aren't afraid of the ground assault."

The UN secretary general, Ban Ki-moon, accused Israel of ignoring calls for restraint. "I regret that despite my repeated urgings, and those of many regional and world leaders together, an already dangerous conflict has now escalated even further," he said.

Israeli troops entered the Gaza Strip at 10.30pm local time on Thursday, under massive supporting fire from air, sea and land.

According to military analyst Alex Fishman, writing in Yedioth Ahronoth: "The tanks, which serve as the heart of the assault force, received an order to open fire at anything that moved. The area and the targets are due to be seized by the morning hours. From here on, [the army] will start to clear the ground, in what could last for several days, depending on political developments."

The initial aim is to destroy tunnels dug by Hamas from Gaza into Israel for the purpose of launching attacks, and to secure and expand the 'buffer zone'' inside Gaza's perimeter in order to prevent short-range rocket launches into Israel.

However, Hamas is likely to attempt to suck Israeli troops deeper into Gaza, increasing the risk of military casualties.

The escalation of the conflict came on the 10th day of military action, a point at which military leaders may have calculated that a limit on what could be achieved by aerial bombardment could be achieved.

The decision to launch a ground invasion was reportedly taken by the security cabinet on Tuesday night, following Hamas' rejection of a ceasefire proposal tabled by Egypt.

But the discovery of a tunnel on Thursday morning, through which a dozen militants were attempting to reach a kibbutz in southern Israel, is thought to have been a deciding factor to go in.

Israel halted bombardment for five hours on Thursday to allow people in Gaza to restock with food and cash and visit relatives.