The ball is in the Hamas court as they have had the option to put a stop to them mess they created for the last 5 months, by laying down their arms and releasing the hostages. If Hamas did not have a choice it is one thing, but they do have a choice.
UNRWA had to know what Hamas was up to. UNRWA has over 30,000 employees, most of them Palestinian and a small number of international staff–Source: UNRWA website— It is easy enough to verify by going to their website.