AMMAN (Reuters) - The U.S. military has moved a new truck-mounted, long-range rocket launcher from Jordan to a U.S. base in Tanf, Syria, near the Iraqi and Jordanian borders, stepping up its presence in the area, two regional intelligence sources said on Wednesday.

They said the (High Mobility Artillery Rocket Systems - HIMARS - had moved into the desert garrison, which has seen a buildup in recent weeks as tensions escalate after the U.S.-led coalition struck Iranian-backed forces to prevent them advancing toward the Tanf base.

“They have arrived now in Tanf and they are a significant boost to the U.S. military presence there,” one senior intelligence source said, without elaborating. The HIMARS had already been deployed in northern Syria with U.S.-backed forces battling Islamic State militants, he added.

Washington deployed the HIMARS on the Turkish border to strike at Islamic State outposts. They were used several times from the Jordanian border to hit militants who had a foothold in the southeastern desert.

Under heavy pressure, the militants have mostly retreated from the desert in the last three months. Now U.S.-backed Syrian rebels are competing with the Syrian army and Iranian-backed militias as they all try to recapture territory from Islamic State.

Tanf is near a Syria-Iraq border crossing on the main Baghdad-Damascus highway. The rebels took it from Islamic State last year, partly to stop Iran from using it to send arms to the Syrian government.

The rebels also want to use it to take more territory along the border and to push toward Deir al-Zor, a large city on the Euphrates where the government has an enclave surrounded by Islamic State fighters.