More than 380 people have been killed, including at least 61 women and children, in four consecutive days of Israeli bombardment and local hospitals are saying they are unable to cope with any more casualties.
"We are ready to deepen and widen the operation in order to make sure that the calm and tranquility will come back to the region"
Israeli defence minister
On Tuesday the soaring death toll and mounting international protests led to calls from the United Nations and the European Union for both sides to agree to a 48-hour humanitarian ceasefire.
But Israel's defence minister, Ehud Barak, said that stronger action may be yet to come.
"We are ready to deepen and widen the operation in order to make sure that the calm and tranquility will come back to the region," he said.
"We believe that this is our primal contract with our citizens to protect them against terrorist attacks."
His comments were echoed by Israel's interior minister who said there would be no let up until the threat of Palestinian rockets attacks from the Gaza Strip had been removed.
"There is no room for a ceasefire," Meir Sheetrit told reporters, adding that the Israeli military would not stop its operations "before breaking the will of Palestinians, of Hamas, to continue to fire at Israel."
Four Israeli citizens have been killed by missiles fired from Palestinian positions since the Israeli offensive on Gaza began on Saturday.
The Israeli army has been massing infantry and armoured forces along the border amid increasing fears that a ground invasion is planned.
Matan Vilnai, Israel's deputy defence minister, said the military "has made preparations for some long weeks of action".
On Monday, areas of the border were declared "closed military zones" and thousands of reservists have been called up by the Israeli military.
"The ground forces are ready," Avital Leibovitz, an Israeli military spokeswoman, said on Tuesday.
"The option exists. It is possible that we will apply it but for the moment we are only hitting from the air and the sea."
Al Jazeera's Ayman Mohyeldin, reporting from Gaza Strip, said that the confirmation that naval vessels were now launching attacks was a further widening of the offensive.
"We undertsand they are targeting buildings and various other targets throughout Gaza," he said.
Mohyeldin said that a ground offensive would worsen the humanitarian situation for Gazans.
"A ground offensive will mean urban warfare, close proximity fighting from street-to-street ... Gaza is so densely-populated that ultimately in that kind of operation the civilian population will find themselves caught in the middle," he said.
More than 1,600 Palestinians have already been wounded in the assault and hospital are running out medicines and other products needed to treat them.
Ban Ki-Moon, the UN secretary-general, has added his voice to calls for an end to the violence.
"All this must stop," Ban told a news conference at UN headquarters in New York.
|Israel says its ground forces are ready to act if it decides to enter Gaza [EPA]
"Both Israel and Hamas must halt their acts of violence and take all necessary measures to avoid civilian casualties. A ceasefire must be declared immediately. They must also curb their inflammatory rhetoric."
Mark Regev, an Israeli government spokesman, told Al Jazeera that the Israel military was was being "as surgical as it can be", while Hamas rocket attacks indiscriminately targeted civilians.
"We have been hitting Hamas command-and-control, Hamas military structures ... our target is not the innocent people of Gaza, it is only the Hamas military machine," he said.
"Our feeling towards the people of Gaza is not hostility, we see them as victims of the terrible Hamas Taliban-type regime, just as the people of southern Israel are victims."
Support for Israel came from the US, with the White House saying Hamas must halt cross-border rocket fire.
"In order for the violence to stop, Hamas must stop firing rockets into Israel and agree to respect a sustainable and durable ceasefire," Gordon Johndroe, a White House spokesman said.