Jordan on Monday sentenced four people to two years in jail each for having tried to join the ranks of the Islamic State group and for promoting the jihadists online.

The kingdom is one of five Arab nations that joined a US-led air campaign against the Sunni extremist group that has declared a "caliphate" straddling the borders of neighbouring Iraq and Syria.

Since the start of the campaign in September 2014, Jordan has reportedly arrested dozens of suspected IS sympathisers and put several on trial.

The state security court, a military tribunal, found the four guilty of engaging in "propaganda on behalf of a terrorist group" and of trying to "join the ranks of armed and terrorist organisations".

The suspects, all in their early 20s, had denied the accusations against them.

Their charge sheet indicated one of them had tried to sneak across the border into Syria to join the jihadist group but was arrested by Jordanian security forces before being able to do so.

The others used social media networks to promote IS.

Jordan has borders with both Syria and Iraq and has reinforced security along its frontiers since the conflict erupted in Syria four years ago.