I came across this claim in this tweet that says, "90% of Palestinians in Gaza are now displaced and homeless, that's over 1.9 million people! ...". Searching for it online, the first result lead me to this YouTube video repeating this claim - 90% of Gaza is homeless. An Huffpost article on Yahoo News says:
Roughly 90% of the Gazan population is now displaced. Aid, food and clean water are scarce, and people are unable to find shelter as Israeli bombardment continues to rain on civilians.
The Seattle Times repeats something similar:
About 90% of Gaza’s 2.3 million people have been displaced within the besieged territory, where United Nations agencies say there is no safe place to flee.
(I've also come across a news article mentioning "70% are homeless" and another saying "80% are displaced and homeless").
Many media article seem to be repeating this claim but do not mention the source. What is the original source of this claim? Which figure is the most accurate?