* Jordan hints vehicles hit were driven by Syrian rebels
* Rise in infiltration attempts from Syria worries Amman (Adds details, army statement, Syrian denial)
By Suleiman Al-Khalidi
AMMAN, April 16 (Reuters) - 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.
A Jordanian security source said the targets appeared to have been Syrian rebels with machine guns mounted on civilian vehicles who were seeking refugee from fighting with government forces in southern Syria, but refused to elaborate.
The Syrian state news agency SANA said no Syrian vehicles were involved in the incident. "What was targeted by the Jordanian air force does not belong to the Syrian army," a military source was quoted by SANA as saying.
"There was an attempt to infiltrate across the border from Syria by a number of vehicles," said Jordanian government spokesman Mohammad al-Momani, also a cabinet minister.
A Jordanian army statement said the incident took place at around 10:30 a.m. (0830 GMT) when several camouflaged vehicles attempted to traverse rugged frontier terrain and disregarded warnings not to proceed.
"After repeated warnings that (we) would not allow a violation of the border, a number of air force planes sent warning shots towards the vehicles, but they did not heed these warnings and continued," the statement said.
"This forced the army to apply known engagement rules and to destroy the vehicles," it said.
Rebels dominate swathes of territory along Syria's southern border with Jordan but have been engaged in sometimes heavy fighting with Bashar al-Assad's forces in the region.
"ABSENCE OF SECURITY" ALONG BORDER
Momani said the kingdom was increasingly worried about incursions 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.
Unlike Syria's other main neighbours Turkey, which has given rebels a safe haven, and Lebanon, whose border has been breached with impunity by combatants, U.S.-allied Jordan has prevented any free flow of arms or fighters over its frontier.
Western diplomats say Jordan has been granted hundreds of millions of dollars from Washington in the last two years o beef up its boundaries with Syria. Amman has constructed scores of observation towers with the latest surveillance equipment.
The kingdom has also been sending more jihadists returning from Syria to speedy trials in military courts in a tougher policy towards its citizens who join Islamist insurgent groups that have taken a leading role in fighting Assad.
Jordan has diplomatically sought to distance itself from calls to bring down Assad. It retains diplomatic and economic ties with Damascus, saying it seeks a political solution to the conflict and opposes foreign military intervention.
Amman has long been concerned that any overt support of the Syrian insurgency could trigger retribution against the kingdom by Assad's powerful security forces.
Jordan's intelligence establishment has long expressed concerns about sleeping cells recruited by Assad in the kingdom with orders to engage in acts of sabotage in reprisal for any perceived support for an Western led military operation against Syria launched from Jordanian territory.
Rebels in Syria say the support that has been given by Amman to moderate anti-Assad brigades has been minimal and insufficient for them to turn the tables in the largely stalemated conflict. (Editing by Mark Heinrich)