The UN said Tuesday the number of Syrian refugees flooding into Jordan had suddenly fallen from several thousand a day to close to zero, warning that fighting may be blocking people in need from coming.
"In Jordan in the last four days, we have seen a significant drop in the number of (Syrian) refugees arriving," Panos Moumtzis, who heads the UN refugee agency's response to the Syria crisis, told reporters in Geneva.
He pointed out that since February, between 1,000 and 3,000 refugees had crossed the border every day, but that "in the last four nights, this number has dropped to almost zero," with only between five and nine people crossing each day.
"This is a situation where we are looking at and monitoring very closely to see what the impact is and what is the reason behind this movement," Moumtzis said.
"If the problem is that people are not being allowed to move, (we want to know) is it security or something else," he said.
UNHCR does not have any staff on the Syrian side of the border, but staff members in Jordan could hear increased fighting and were hearing reports from people crossing that battles in the area were intensifying, especially at night.
"Something is happening there," Moumtzis said, pointing out that while it remained unclear why the refugees had stopped coming, UNHCR was in contact "with everyone" to ensure that "people are able to cross without facing difficulty to reach safety wherever they are."
Syrians have surged out of their country since March 2011, when a crackdown on protests against the regime of President Bashar al-Assad heralded the start of an armed rebellion.
More than 90,000 people have been killed since then, while over 1.5 million Syrians have fled to neighbouring countries, including some 474,000 who have been registered or are awaiting registration in Jordan, according to UN figures.
Another 6.8 million people are in need of assistance inside Syria, including nearly 4.3 million people who have been displaced from their homes.
That means that, all told, around 38 percent of Syria's pre-war population of 22.5 million are in need of humanitarian assistance, Moumtzis pointed out.