Israel vowed Thursday to keep its troops in Gaza until they finish destroying a network of cross-border tunnels, despite sharp U.N. and U.S. criticism over the Palestinian death toll that hit 1,435.

Speaking at a cabinet meeting in Tel Aviv, Prime Minister Benjamin Netanyahu said he would not accept any ceasefire that did not allow troops to continue destroying tunnels used by militants to attack Israel.

Britain is "gravely concerned" by the high number of civilian casualties resulting from Israel's military operation in Gaza, Foreign Secretary Philip Hammond said on Thursday. 

Speaking on his first official visit to the region since taking over as Britain's top diplomat, Hammond said London would do everything it could to help broker a quick end to the hostilities which have so far claimed the lives of more than 740 Palestinians in Gaza, 34 Israelis, mainly soldiers, and a Thai worker. 

U.S. Secretary of State John Kerry spoke Thursday to his counterparts in Qatar and Turkey, which support the Palestinian Islamist group Hamas, as he pressed for a Gaza ceasefire.

Kerry -- who is in Egypt, which has drafted a truce proposal for the Israel-Hamas conflict -- spoke by phone with the foreign ministers of Qatar and Turkey, a U.S. official said.

Secretary of State John Kerry told Israeli Prime Minister Benjamin Netanyahu on Tuesday that a U.S. ban on flights to Israel was solely due to safety concerns.

Airlines blocked flights to Israel Wednesday after a Gaza rocket struck near airport runways, as the U.N. chief urged an end to a conflict that has killed 639 Palestinians and 31 Israelis.

As the violence entered its 16th day, neither Israel nor Islamist movement Hamas appeared willing to end hostilities, despite days of diplomatic efforts to coax them into a truce.

Israeli Prime Minister Benjamin Netanyahu spoke Friday of bolstering his ground assault on Gaza in what commentators said was part of a strategy to pressure Hamas into a truce.

"My instructions and those of the defense minister to the military, in accordance with security cabinet's approval, is to prepare for the possibility of a significant broadening of the ground activity," he told ministers at a special cabinet session at the defense ministry in Tel Aviv.

Israeli Prime Minister Benjamin Netanyahu said Friday he had ordered the military to prepare for a possible significant expansion of the ground operation against Gaza militants.

In his first public remarks since the operation began late on Thursday, Netanyahu said air strikes alone could not deal a significant blow to the network of tunnels used by Hamas militants to stage cross-border attacks on southern Israel. 

The death toll from Israel's week-long campaign in Gaza rose Tuesday to 194, as two Palestinians were killed in renewed strikes after an Egyptian truce bid failed.

An Israeli was also killed on Tuesday, the first since the eruption of the war.

Italian Foreign Minister Federica Mogherini will on Tuesday visit an Israeli town hit by rocket strikes from Gaza and meet Palestinian president Mahmud Abbas as part of a diplomatic push for peace, her ministry said.

Mogherini "will be in Ramallah this afternoon to meet president Mahmud Abbas and foreign minister Riyad al-Malki", the ministry said in a statement.

U.S. Secretary of State John Kerry on Sunday phoned Israeli Prime Minister Benjamin Netanyahu to renew a U.S. offer to help mediate a truce as Israel stepped up its military campaign against the Gaza Strip.

Kerry "highlighted the U.S. concern about escalating tensions on the ground," a senior State Department official said.