(Reuters) - beefed up its border defenses with Sunday after Sunni gunmen seized territory close to its border in Anbar province and appeared to have also taken control of the only land crossing with its large eastern neighbor, officials and witnesses said.

Two officials said the border crossing almost 575 km (357 miles) from the Iraqi capital and nearly 320 km (199 miles) from was effectively closed after Sunni gunmen took control of the crossing.

A Jordanian minister earlier told Reuters traffic had halted and there were signs of chaos at the crossing that serves as a major artery for passenger and trade flows between the two countries.

"The last traffic was around 7:30 p.m. (1630 GMT) and border officials are saying the situation is not normal on the other side of the border," Minister of State for Media and Communication said.

Earlier, Iraqi Sunni gunmen had seized control of the town of , just 90 miles (145 km) east of the border with .

An source confirmed units had been put in a state of alert in recent days along the 181-km (112-mile) border with , redeploying in some areas as part of steps to ward off "any potential or perceived security threats".

Truck drivers who arrived in before traffic halted after crossing the border said Sunni tribal militants were now running and manning checkpoints along large stretches of the Baghad- highway that runs through the crossing.

A security source who requested anonymity said the border crossing on the Iraqi side had fallen earlier in the day to local Sunni tribal gunmen who permitted customs officials to continue to run it administratively until later on Sunday.

U.S. ally was expected to formally close the border to traffic as soon as the formally announced its loss of control over the crucial trade and passenger crossing, he added.

On Sunday, militants overran a second frontier post on the Syrian border, extending two weeks of swift territorial gains as the Islamic State of and the Syria pursues the goal of its own caliphate straddling both countries.

ISIL thrust east from a newly captured Iraqi-Syrian border post on Sunday, taking three towns in 's western Anbar province after seizing the frontier crossing near the town of on Saturday, witnesses and security sources said. They seized a second, al-Waleed, on Sunday. The gains have helped ISIS secure supply lines to where it has exploited the chaos of the uprising against President to seize territory.

The loss of the Iraqi border crossing with was not seen as an immediate security threat to the kingdom although some were unnerved by the prospect of al Qaeda-affiliated groups along the border with , another official said.

It was difficult to see security-conscious , which has almost cut off any flow of militants across its heavily sealed northern border with , allowing itself to become a launching pad or supply route for Islamist jihadists into , he added.

, grappling with the mounting impact of the grinding conflict in neighboring , is one of the closest U.S. allies in the .