MOSCOW, Sept. 17 (Xinhua) -- Russia and Turkey have decided to set up a demilitarized zone between the armed opposition and the government troops in Syria's Idlib province by Oct. 15, Russian President Vladimir Putin said Monday.

The demilitarized zone with a depth of 15-20 kilometers will be created along the contact line of the armed opposition and the government forces, Putin said at a joint press conference following talks with his Turkish counterpart Recep Tayyip Erdogan in Russia's Sochi.

Mobile patrol groups consisting of Turkish army units and Russian military police units will control the situation in the demilitarized zone, Putin said, according to a Kremlin press release.

"Russia and Turkey reaffirmed their determination to fight terrorism in Syria in all its forms and manifestations," Putin said.

"We will continue to work on the formation of a constitutional committee consisting of representatives of the Syrian leadership, opposition forces and the civil society," he said.

Territories occupied by the Syrian opposition must be demilitarized, Erdogan said at the press conference, adding that the opposition will remain there but Turkey and Russia will make every effort to eliminate all radical groups from these territories.

There will be no military operation against the armed opposition in Idlib and the Russian military will soon coordinate with the Syrian forces, Russian Defense Minister Sergei Shoigu said following the Putin-Erdogan meeting.

The Syrian government forces backed by Russia and Iran were preparing an offensive against the rebels' last major stronghold in Idlib, although Turkey and the United States have repeatedly warned against any operation.

Ankara and Washington reject the possible offensive in Idlib, citing that it could cause great civilian casualties and even a humanitarian disaster.

However, Erdogan's call for a cease-fire in Idlib, which borders Turkey, was accepted neither by Russia nor Iran at the tripartite summit in Tehran on Sept. 7.