Jordan has turned away thousands of Syrian refugees in the past week in the first such clampdown since the crisis in Syria began more than two years ago, diplomats, activists and aid workers said on Tuesday, May 21, according to Reuters.

Jordan, due to host an international conference on Syria on Wednesday, has already taken in 473,587 Syrians out of a total of 1.5 million who have fled the conflict in an exodus that has accelerated in the past four months, U.N. figures show.

All four unofficial crossing points used by refugees trying to escape bombardments in the southern province of Deraa have been closed for the past six days, refugees and aid workers say, although the official frontier post at Jaber remained open. They said Syrian families trying to pass into Jordan from the rebel-held border villages of Nasib and Tel Shehab had been turned away with no reason given by the Jordanians.

A Western diplomat linked the closure to security measures before Wednesday's "Friends of Syria" meeting in Amman, where foreign ministers of Western and Gulf states opposed to Assad will discuss the quest for a political solution in Syria.

Resource-poor Jordan has long sought to win more outside help in its struggle to cope with the vast influx of refugees.

The head of the U.N. refugee agency in Jordan, confirmed to Reuters that the refugee flow had slowed to a trickle in the last few days, but said the reasons were not clear. He said fewer than 30 refugees had arrived in the last three days, compared to the usual 1,000 to 2,000 a day.