Fighting broke out between Jordanian and Syrian forces in a border region between the two countries late on Friday, but a Jordanian source said no one on Jordan's side appeared to have been killed.
It was the most serious incident between the two countries since the uprising in Syria against President Bashar al-Assad began 17 months ago.
A Syrian opposition activist who witnessed the fighting said armoured vehicles were involved in the clash in the Tel Shihab-Turra area, about 80 km (50 miles) north of the Jordanian capital Amman, that occurred after Syrian refugees tried to cross into Jordan.
"The Syrians fired into Jordan at 10.30 pm 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.
A Jordanian source, speaking on condition of anonymity, said: "The Syrian side fired across the border and fighting ensued. Initial reports indicate that there has been no one killed from the Jordanian side."
Tens of thousands of Syrians have crossed into Jordan since the start of the uprising.