Jordanian warplanes hit and destroyed several vehicles trying to cross the border from Syria, a government spokesman said on Wednesday, underlining Amman's concern about incursions from areas controlled by Syrian rebels.

"There was an attempt to infiltrate across the border from Syria by a number of vehicles," said spokesman Mohammad al-Momani, also a cabinet minister, told Reuters.

A Jordanian security source said the targets were Syrian rebels in civilian cars mounted with machine guns.

It was unclear whether rebels who have dominated swathes of territory along Syria's southern border with Jordan might have been seeking refuge inside Jordan from fighting with President Bashar al-Assad's forces that has raged in the region.

Momani said the kingdom was increasingly worried about infiltration from Syria. "We are worried about cases of infiltration ... and reports that talk about armed groups that are close to the border and the absence of security there."

Amman has tightened already firm controls along the 370-km (230 mile) border to try to prevent Jordanian Islamist militants who have joined the rebels from crossing back into Jordan. They are seen as a domestic security threat. - Reuters