Donald Trump has opted to end the CIA's covert programme to arm and train moderate anti-Assad rebels in Syria, according to US officials. The move has been long sought after by Russia, the Syrian government's biggest ally.

Supporters of the programme, which was central to the Obama administration's Syria policy, have questioned how effective it is since Russia's arrival in Syria in 2015, The Washington Post reported.

Although the Trump administration has noted it does not see envision peace in the area with Bashar al-Assad in power, Trump has also expressed interest in working with Russia to find a solution to the ongoing conflict.

Moscow sees the programme as an assault on its interest in the area.

US officials said Trump decided to end the secret programme nearly a month ago, following an Oval Office meeting with CIA director, Mike Pompeo, and national security adviser HR McMaster. The meeting was held ahead of Trump's 7 July meeting with Russian President Vladimir Putin in Germany.

Following the Trump-Putin meeting, Washington and Moscow announced an agreement to support a new cease-fire in southwest Syria, the Post reported. Trump lauded the limited ceasefire agreement as a benefit of working with Moscow.

US officials noted that the decision to end the covert programme to arm the Syrian rebels was not a condition of the cease-fire negotiations. However, current and former officials who support the programme suggest the move is a major concession to Russia.

"This is a momentous decision," a current official, who spoke on the condition of anonymity, to the Post. "Putin won in Syria."

One analyst said the end of the programme will likely empower more radical rebels and affect the credibility of the US, according to the Post. "We are falling into a Russian trap," Charles Lister, a senior fellow at the Middle East Institute, said. "We are making the moderate resistance more and more vulnerable....We are really cutting them off at the neck."

US involvement will not cease with the end of the CIA programme. It still leads a vigorous air campaign against Isis and the Pentagon will continue to run its train-and-equip programme to support a largely Kurdish rebel force that is advancing on Raqqa.

According to the Post, senior US officials say the CIA programme will be phased out over a period of months. Some support could also be redirected to other missions.

"This is a force that we can't afford to completely abandon," said Ilan Goldenberg, a former Obama administration official and director of the Middle East Security Program at the Center for a New American Security. "If they are ending the aid to the rebels altogether, then that is a huge strategic mistake."