Rebels fighting to oust Syrian President Bashar al-Assad's regime on Monday sealed off the country's only two border posts with Jordan, a military official said.
"The Free Syrian Army closed the two crossings of Daraa and Naseeb from their side after they took control of them," the Jordanian official told AFP on condition of anonymity.
He declined to elaborate.
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"Jordan is monitoring the Syrian crisis and any decision will be taken in line with our national interest," Information Minister Samih Maaytah told state-run Petra news agency.
"Jordan did not take any decision to close the border. There is nothing new on the Jordanian side of the borders," said Maaytah, who is also government spokesman.
The development comes after the rebels seized a 25-kilometre (15-mile) strip of land stretching from the Jordanian border to the Israeli-occupied Golan Heights, according to the Syrian Observatory for Human Rights.
Jordan has become home to more than 450,000 refugees from the two-year-old conflict in Syria.