Syria's foreign minister said on Monday that Syrian forces stand ready to fight Islamist militants around the northwestern region of Idlib if a Russian-Turkish deal is not implemented there the same day, in keeping with a critical deadline.

The deal for Idlib sets up a buffer zone running 15-20 km (9-13 miles) deep into rebel territory that must be evacuated of all heavy weapons and all Islamist militants by Monday.

Foreign Minister Walid al-Moualem said it was up to Russia now to judge whether the agreement, which staved off a government offensive on the last notable swathe of territory in insurgent hands after seven years of war, was being fulfilled.

"Our armed forces are ready around Idlib to eradicate terrorism if the Idlib agreement is not implemented," al-Moualem said at a press conference with his Iraqi counterpart Ibrahim al-Jaafari in Damascus.

"Idlib, as any other province, has to return to Syrian sovereignty. We prefer to have it through peaceful means, through reconciliation, but if not there (are) other options."

Tahrir al-Sham, an alliance of Islamist militants spearheaded by al Qaeda's former Syrian affiliate, signalled on Sunday that it would abide by the terms of the deal, although it did not explicitly say so.

"We value the efforts of all those striving - at home and abroad - to protect the liberated area and prevent its invasion and the perpetration of massacres in it," Tahrir al-Sham said in its statement. However, it added that Tahrir al-Sham would not end its jihad or hand over its weapons.

Idlib's other main rebel faction, a Turkish-aligned alliance of groups known as the National Liberation Front, has already expressed its support for the agreement.

Moualem further said the government's next target after recovering Idlib from rebels would be the area east of the Euphrates, indicating territory held by the Kurdish-led and U.S.-backed Syrian Democratic Forces (SDF).

"After Idlib our target is east of the Euphrates," he said, adding that the area must also return to Syrian sovereignty.