The UN Secretary-General said he was horrified by the killing of hundreds of civilians following a strike on a hospital in Gaza on Tuesday.

In a tweet, António Guterres strongly condemned the strike, adding that his heart is with the families of those who died.

Mr. Guterres stressed in his message on X that hospitals and all medical personnel are protected under international law.

He condemned the strike and an attack earlier on Tuesday on a school run by the UN agency that assists Palestine refugees, UNRWA, which killed at least six people, his spokesperson said in a statement.

The UN human rights chief described the strike on the hospital as "totally unacceptable".

"We don't yet know the full scale of this carnage but what is clear is that the violence and killings must stop at once," said High Commissioner Volker Türk in a statement.

Displaced civilians were reportedly seeking shelter at the hospital, following Israel’s order to evacuate to the south in advance of what is expected to be a ground assault.

“WHO strongly condemns the attack,” agency chief Tedros Adhanom Ghebreyesus wrote in a post on the social media platform X, formerly Twitter.

“We call for the immediate protection of civilians and healthcare, and for the evacuation orders to be reversed,” he added.

Human rights chief Türk said hospitals are sacrosanct and must be protected at all cost, adding that "those found responsible must be held to account.”