A military tribunal jailed six Muslim extremists Wednesday for trying to join the Al-Qaeda-linked Al-Nusra Front to fight against Syrian President Bashar al-Assad's forces, a court official said.

"The state security court sentenced the six Salafist men to two and a half years in jail each for attempting to infiltrate Syria and join Al-Nusra and fight the Syrian regime," he told AFP.

Salafists espouse an austere form of Sunni Islam.

"The convicts, arrested in December as they tried to cross the border, were charged with carrying out acts that would expose Jordan and its citizens to the risk of acts of aggression and revenge," the official added.

The same court on Monday sentenced a Jordanian man to two and a half years in prison for joining Al-Nusra.

Jordan, which is hosting more than 500,000 Syrian refugees, has jailed dozens of men convicted of trying enter Syria to fight alongside rebel forces.

Amman denies accusations from the Syrian regime that the kingdom has opened up its borders to jihadist fighters.

On Monday, Britain's Daily Telegraph cited a study by consultancy IHS Jane's as showing that jihadists and members of hardline Islamist groups make up almost half of forces fighting against Assad -- estimated at about a total of 100,000.

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