Jordanian and Syrian security forces have clashed in a border region between the two countries, a Jordanian source said.
The fighting broke out late on Friday after Syrian troops reportedly fired on Syrian refugees crossing the border into Jordan.
"The Syrian side fired across the border and fighting ensued. Initial reports indicate that there has been no one killed from the Jordanian side," said the Jordanian source, speaking on condition of anonymity.
A Syrian opposition activist who witnessed the fighting said armoured vehicles were involved in the clash in the Tel Shihab-Turra area, about 80km north of the Jordanian capital Amman, that occurred after Syrian refugees tried to
cross into Jordan.
"The Syrians fired into Jordan in pursuit of refugees and the Jordanians responded. The fighting escalated
and Jordanian armoured vehicles hit two Syrian border guard outposts," said the activist, giving his name only as Abdallah.
"The fighting was intense for an hour and now it is intermittent," he said.
It was the most serious incident between the two countries since the uprising in Syria against President Bashar al-Assad began 17 months ago.
Jordanian troops have fired near the border in the past to stop Syrians from shooting at fleeing refugees.
Syria's long border with Jordan has been an escape route for opponents of Assad, including Prime Minister Riad Hijab who defected this week.