DAMASCUS (Dispatches) – U.S. marines have held eight days of unprecedented military exercises with terrorists in southern Syria in an attempt to send a "strong message” to Iran and Russia, a senior military official said Thursday. U.S. military spokesman Colonel Sean Ryan described the drills as "a show of force,” saying that the Pentagon had notified Russia through "deconfliction” channels to prevent "miscommunication or escalate tension”. "The exercise was conducted to reinforce our capabilities and ensure we are ready to respond to any threat to our forces within our area of operations,” he said. Muhanad al-Talaa, commander of the Pentagon-backed Maghawir al-Thawra group, told Reuters the drills this week at the U.S. military outpost in Tanf were the first such exercises with live-fire air and ground assault involving hundreds of U.S. troops and terrorists. The Tanf base is located near Syria's borders with Jordan and Iraq. Russia and the Syrian government have repeatedly called on Washington to pull out its troops from the Tanf base, where it has declared a 55km-radius "deconfliction zone" off-limits to others. Terrorists say hundreds of U.S. Marines arrived this month in Tanf to join special operations troops already based in the garrison and participate in the drills, amid heightened U.S.-Russian tensions in Syria and a naval buildup in the Mediterranean. The U.S. says the "deconfliction zone" has become a safe haven for at least 50,000 "civilians” who live in the Rukban camp that lies within it. Russia's defense ministry in August said Washington has been harboring Daesh terrorists within the zone. "We are staying whether the Russians or Iranians want or not," the terrorist commander added. Tanf lies on the strategic Damascus-Baghdad highway and is surrounded by desert. U.S. warplanes have struck Syrian troops on several occasions to prevent them advancing, in what Washington has described as self-defense. This makes the base part of a larger American campaign to expand its outreach in the Middle East. Terrorists say the U.S. military's new policy to bolster Tanf's capabilities is a big shift. U.S. President Donald Trump has repeatedly vowed to pull U.S. troops out of Syria in spite of apparent opposition from the Pentagon. Still, no major change has occurred in the U.S. military position in the war-torn country since he made that pledge earlier this year. Meanwhile, Jordan and Syria held their first technical talks on opening a major border crossing in southern Syria that was recaptured from terrorists in July, a Jordanian official said on Thursday. Damascus hopes to reopen the Nassib route, which is vital to its hopes of reviving Syria's shattered economy and rebuilding in territory now under its control. Amman also hopes the opening of the border crossing will reactivate billions of dollars of annual transit trade between Europe and Persian Gulf markets across Syria. The official told Reuters the meeting that was requested by Syria was held on Wednesday at the Jaber crossing, on the Jordanian side of the border, where technical teams began talks on the practical arrangements from customs to security needed to reopen the crossing. The crossing's recapture by Syrian forces in July was a main goal of a military campaign launched in June to regain control of terrorist-held parts of the southwest.