The United Nations has said reports about a possible decision to expand Israel's military operations throughout the Gaza Strip are "deeply alarming" if true.

UN Assistant Secretary-General Miroslav Jenca told a UN Security Council meeting on the situation in Gaza that such a move "would risk catastrophic consequences... and could further endanger the lives of the remaining hostages in Gaza.

"International law is clear in the regard; Gaza is and must remain an integral part of the future Palestinian state," he added.

Israeli Prime Minister Benjamin Netanyahu met senior security officials on Tuesday to finalise a new strategy for the nearly two-year-old war in Gaza with media reporting he favoured a complete military takeover of the Palestinian enclave.

Responding to the reports at the Security Council, China's deputy UN representative, Geng Shuang, said: "We urge Israel to immediately halt such dangerous actions."

He called for a ceasefire and urged countries with influence to take concrete steps to help bring one about.

Speaking to new recruits at a military base, Netanyahu said Israel must "complete" the defeat of Hamas in Gaza to secure the release of the remaining hostages.

"It is still necessary to complete the defeat of the enemy in Gaza, release our hostages and ensure that Gaza never again constitutes a threat to Israel," Netanyahu said.

"We are not giving up on any of these missions."

The brother of Israeli hostage Evyatar David, who was shown appearing emaciated in a video released by Hamas last week, told the Security Council to use its leverage to secure the immediate unconditional release of remaining hostages and to ensure humanitarian aid reaches them.

"Every moment of delay is a step closer to final tragic outcome," Ilay David told the meeting.

He said the video showed his brother as "a living skeleton. He had barely the strength to move or speak, his voice barely recognizable," the brother said, adding that neither he nor his mother could bring themselves to watch.

"We knew that if we did, we would be unable to function. My father and sister, however, felt they had to see him, to hear his voice, to feel him somehow. Now these images haunt them. My father cannot sleep, and my mother has not stopped crying ever since," he said. (Agencies)