GENEVA (AP) — U.N. officials said Tuesday that the number of Syrian refugees arriving in Jordan has suddenly fallen from an average of 2,500 a day to fewer than 20, and they are trying to quickly figure out why.

Millions of people have been displaced in Syria as the civil war there has engulfed large areas, and Jordan has become a main refuge for Syrians who choose to flee their country. U.N. officials said they are unsure what has led to the drop in the flow of refugees to Jordan this week, and because they lack staff on the Syrian side of the border they cannot observe the situation there.