"We have seen the reports and we will need more time and access to be able to investigate this at the moment," Ravina Shamdasani, spokesperson for the UN high commissioner for human rights, told a press conference in Geneva.

Noting that they have "no" information" to share on this matter, Shamdasani added: "It would be important to do a proper investigation to understand what has happened."

The official said she would not speculate on the consequences if they confirm the use of white phosphorus.

The Human Rights Watch (HRW) late Thursday said it verified videos showing multiple airbursts of artillery-fired white phosphorus over Gaza and Lebanon on Oct. 10-11.

"Israel’s use of white phosphorus in military operations in Gaza and Lebanon puts civilians at risk of serious and long-term injuries," the HRW said.

It said white phosphorus has a significant incendiary effect that can severely burn people and set structures, fields, and other civilian objects in the vicinity on fire.

"The use of white phosphorus in Gaza, one of the most densely populated areas in the world, magnifies the risk to civilians and violates the international humanitarian law prohibition on putting civilians at unnecessary risk," it added.

'Civilians must never be used as bargaining chips'

Shamdasani stressed "civilians must never be used as bargaining chips," adding: "Yet, we continue to receive heartbreaking messages of helplessness from people in Gaza, who are moving from house to house, terrified, seeking elusive safety."

"And civilians continue to be held hostage by Palestinian armed groups – in clear violation of international humanitarian law. We call, again, for their humane treatment and their immediate and unconditional release," she said.

Regarding the Israel's order for evacuation of Palestinians from northern Gaza within the next 24 hours, she said this order is affecting more than a million Palestinians, including children, older and sick people, forcing them to relocate with little or no transport and with scant guarantees for their safety.

"We echo the secretary-general’s spokesperson’s call for this to be rescinded, avoiding a calamitous situation," she said, referring to the earlier remarks of Stephane Dujarric.

The Israeli army on Friday ordered all residents of northern Gaza to evacuate their homes and head to the south.

In a dramatic escalation of Middle East tensions, Israeli forces launched a sustained and forceful military campaign against the Gaza Strip, a response to a military offensive by the Palestinian resistance group Hamas in Israeli territories.

The conflict began last Saturday when Hamas initiated Operation Al-Aqsa Flood against Israel, a multi-pronged surprise attack including a barrage of rocket launches and infiltrations into Israel via land, sea and air.

Hamas said the operation was in retaliation for the storming of the Al-Aqsa Mosque in occupied East Jerusalem and Israeli settlers' growing violence against Palestinians.

The Israeli military then launched Operation Swords of Iron against Hamas targets within the Gaza Strip.

Israel's response has extended into cutting water and electricity supplies to Gaza, further worsening the living conditions in an area that has reeled under a crippling siege since 2007.