Turkish President Tayyip Erdogan welcomed an agreement between the Kurdish-led and U.S.-backed Syrian Democratic Forces (SDF) and Syria’s new government, saying its full implementation would contribute to security and stability in the country.

The SDF, which controls much of Syria's northeast and which Ankara views as a terrorist organisation because of links to Kurdish militants in Turkey, signed an agreement to join Syria's new state institutions, the Syrian presidency said on Monday.

The accord provides for SDF-controlled civilian and military institutions in northeast Syria to be integrated with the state, and for border crossings, an airport, and oil and gas fields there to come under the Damascus administration's control.

"The full implementation of the agreement reached yesterday in Syria will contribute to the country’s security and stability. The beneficiaries of this will be all our Syrian brothers and sisters," Erdogan said on Tuesday.

"We attach great importance to the territorial integrity of our neighbour Syria, the preservation of its unitary structure, and the strengthening of its unity and stability," Erdogan added in televised comments.

Earlier, a Turkish official said Ankara was "cautiously optimistic" about the deal but focused on its implementation.

The SDF has "made promises before, too, so we are looking at implementation rather than at the expression of intent here," the official told Reuters.

The accord comes at a critical moment for Damascus as it grapples with the fallout from mass killings of Alawite minority members in western Syria - violence that Syrian President Ahmed al-Sharaa said on Monday threatened his effort to unite Syria after 14 years of conflict.

Ankara has become one of the main foreign allies of Sharaa's new Islamist government since rebels - some of them backed over many years by Turkey - ousted former Syrian President Bashar al-Assad last year to end his five-decade rule,

Turkey, which still controls swathes of territory in Syria's north after cross-border operations against the YPG militia that spearheads the SDF, has repeatedly demanded that the YPG disarm and disband, and for any non-Syrian fighters in the militia to leave the country.

The Turkish official said talks at the weekend between Iraq, Syria, Turkey and Jordan in Amman regarding security cooperation between the four countries, including establishing an operations centre, sharing intelligence and handing over prison camps where Islamic States fighters are held by the SDF, were influential in the SDF-Damascus deal being agreed as well.

The official said the Amman talks had conveyed the message that the presence of the YPG in Syria would not be tolerated.

The agreement between the SDF and Damascus also comes after the outlawed Kurdish PKK militant group said earlier this month that it would halt hostilities against the Turkish state, following an appeal from its jailed leader to disarm.

The PKK, which launched an insurgency against the Turkish state in 1984, is designated a terrorist organization by Turkey, the United States and European Union. More than 40,000 people have been killed in the conflict.