ZARQA, Jordan -- Under the watchful eye of stern-faced American advisers, hundreds of U.S.-trained Jordanian commandos fanned across this dusty desert plain, holding war games that could eventually form the basis of an assault in Syria.
With the recent deployment of Patriot missiles near the Syrian border, and the mock Syrian accents of those playing the enemy, the message was clear: There is fear of spillover from the Syrian war in this U.S.-allied kingdom, and the potential for a Jordanian role in securing Syria's chemical weapons stockpiles should Bashar Assad's regime lose control.
Dubbed Eager Lion, the 12-day exercise involves combined land, air and sea maneuvers across the country. It brings together 8,000 personnel from 19 Arab and European nations to train on border security, irregular warfare, terrorism and counterinsurgency.
Marine Corps Lt. Col. Duke Shienle said Syria "is a concern that all our regional partners share."
The Syrian crisis is "causing all military in the region to increase intensity," he said as he supervised masked commandos in black uniforms from Jordan and two other Syria neighbors -- Iraq and Lebanon -- in a mock exercise to free a hijacked aircraft on an airstrip in the eastern Jordanian desert.
Nearby, U.S. military strategists taught Jordanian riot police to quickly contain a mock protest by angry mobs in a crowded refugee camp. The trainers refused to name the camp, but the trainees said it was "Zaatari," a reference to a refugee settlement straddling the border with Syria that shelters around 185,000 displaced Syrians.
"We want freedom! We want a free Syria!" the trainees shouted, speaking the Syrian dialect as they depicted Syrian refugees. Others looked on from under dusty tents pitched on a strip of desert outside a Jordanian army compound. The location of this exercise and others could not be disclosed in line with Jordanian army regulations.
Elsewhere, in the south, hundreds of masked Jordanian commandos in black uniforms used machine-guns, rocket propellers and tanks to overwhelm an enemy target as Jordanian helicopters and fighter jets -- all part of previous American donations -- buzzed the skies overhead.
"We want to tell anyone with malicious intentions toward Jordan that we can hit back where it hurts most painfully," said one Jordanian commando, speaking under scorching sun in the arid mountain region. He could not be named under army regulations and declined to say if the enemy he was fighting was Assad's army.
Other training focused on humanitarian relief and crisis management and involves 7,000 civilians from non-governmental organizations engaged in providing assistance to Syrian refugees, said Tawfiq Hennawi of the International Committee of the Red Cross, one of the participating NGOs.
Jordan hosts more than half a million Syrians who fled Assad's military onslaught and that number is expected to rise to 1.2 million by the end of the year.
"These exercises bolster our defense capabilities," said Jordanian army Maj. Gen. Awni Edwan, adding that the Eager Lion exercises, which end Thursday, are routine, having being held twice before at the same time.
"We don't intend to attack anybody," he said.
Jordan has been leery that Assad may eventually use his chemical weapons against his neighbors, or if his regime starts to collapse, his stockpile may fall into the hands of al-Qaida or other militants who are trying to rise to power in Syria.
There has been mounting speculation that should Assad's regime begin to lose control, Jordan will dispatch its highly-skilled, U.S.-trained and equipped commandos to secure Assad's chemical weapons and create a safe haven for Syrian refugees along the 230-mile (375-kilometer) border with Jordan, according to a Western diplomat who monitors Syria from his base in Jordan.
The purpose is to prevent a further influx of Syrian refugees into Jordan out of fear that Shiite militants from the Lebanese Hezbollah group or other Iranian agents may slip across the border to destabilize this key U.S. ally, said the diplomat, who spoke on condition of anonymity because identifying him might jeopardize his intelligence-gathering on Syria.
Jordan's predominantly Sunni Muslim population is traditionally a fiery critic of the growing influence of Iran and its rival Shiite sect.
Regional media reports this week suggesting that Hezbollah activists are deploying near the Jordanian border to help Assad regain control of southern Daraa province- which has been a lifeline for arms shipments to rebels seeking to topple him - sent jitters across Jordan. Officials said that security was immediately beefed up, with more Jordanian soldiers deployed along the border with Syria.
In recent weeks, Assad's forces have appeared to be regaining control over areas seized by rebels, particularly the strategic town of Qusair.
Jordan also fears that Assad's sleeper cells, including Hezbollah, may already be in the country and would act if instructed by Iran or Syria, where an uprising that started in 2011 has descended into all-out civil war.
Eager Lion coincides with Washington deploying one or two Patriot batteries along the border with Syria and agreeing to keep a squadron of 12 to 24 F-16 fighter jets after the exercises - a move Syria's regime and its Russian patron have expressed concern over.
Russian Foreign Minister Sergey Lavrov was quoted by Russia's Interfax news agency as saying that the deployment of the air-defense systems in Jordan in order to set up a no-fly zone over Syria would be a violation of international law.
The United States has said it has no plans for military intervention in Syria, although President Barack Obama has left the door open for any possibility.
"With this exercise being the biggest fire power show ever in Jordan, coupled with the deployment of Patriot air defense systems and U.S. fighter jets, it is clear that the ground is being set for military intervention in Syria," said Col. Khalil Rawahneh, a Jordanian military strategist who participated in at least 16 U.S. and British-sponsored maneuvers until he retired four years ago.