Assad issued a legislative decree "ending the work" of the original 1968 proclamation that created the courts, the presidency said in a statement.

"All cases referred to the military field courts are to be referred... to the military judiciary," said the statement posted on the Telegram messaging app, adding that the move went into effect immediately.

According to a 2017 report from rights group Amnesty International, the military field court's rules and proceedings "are so summary and arbitrary that they cannot be considered to constitute an actual judicial process".

It said military field court trials take just a few minutes.

It added that thousands of people detained at the notorious Sednaya prison had been killed in mass hangings after "trials" at such a court.

Syrian lawyer Ghazwan Kronfol told AFP the courts' jurisdiction was expanded to civilians in response to unrest in the 1980s.

The courts are not required to follow due process, there is "no role for the lawyer" in the proceedings, and sentences cannot be appealed, he added.

"During the years of the revolution and armed conflict, a lot of detainees have been sentenced to death in these courts" and their executions carried out as soon as the sentences were approved, he added.

Syria's civil war broke out in 2011 with the government's repression of peaceful protests.

"Thousands may have been executed according to rulings from those courts," Kronfol added.

An activist who declined to be identified due to security concerns also estimated that thousands or "maybe even tens of thousands" had died due to the military field courts.

Sunday's decision was "long overdue" but "should be treated with caution... particularly because the regime has never acknowledged that these courts violate detainees' human rights" and can still detain people without trial, the activist added.

Diab Serriya, from the Association of Detainees and the Missing in Sednaya Prison, said that "if detainees are referred to military courts" instead of military field courts, "they will at least be allowed a lawyer".

"Around 70 percent" of detainees at the Sednaya facility after 2011 "went before the military field court, which handed most of them death sentences", he said.

He expressed hope that if the military field courts are closed and their archives can be accessed, families will be able to know "the fate of their loved ones who have been missing and forcibly disappeared for years".