Turkey is in agreement with the U.S. to block the Democratic Union Party (PYD) from a ISIS-free "safe zone" in northern Syria, according to Turkish diplomatic sources. The PYD is a Syria-based affiliate of the Kurdistan Workers' Party (PKK) which is considered a terrorist organization by Turkey, the U.S. and the EU. Diplomatic sources also stated that the number of U.S. aircraft to land in Turkey's southern Incirlik air base, which has recently been made available to the U.S.-led anti-ISIS coalition, would increase in the coming days. Joint operations will also follow at a proper time, said the sources. The Turkish Foreign Ministry announced on July 29 the decision to allow the use of Turkey's air bases by the coalition aircraft, meaning the Incirlik base "could be used any time, whenever needed". Both Turkey and the U.S. have reportedly warned the PYD not to cross to the west of the Firat (Euphrates) River. They were also warned not to proceed to any demographic change in the region and allow the return of Syria's Turkmen and Arab population, which had previously left their home because of fighting with ISIS, still according to Turkish officials who wished to remain nameless. Turkish diplomatic sources said the zone to be cleared of ISIL will be made "safe" after the joint operation. Moderate Syrian opposition forces are to be deployed in what Turkey calls a "safe zone". The U.S. however maintained Tuesday that it does not view efforts to clear ISIS from the northern Syrian border as a bid to create a "safe zone." "We've been very careful not to put monikers or descriptions describing what this area is going to look like except to say our effort is focused on driving ISIS out of the region," State Department spokesman Mark Toner said. The Turkish officials also said stated that the train-and-equip program for the Syrian opposition was underway. The train-and-equip program, jointly organized by the U.S. and coalition partners, is intended to help prepare Syrian opposition fighters in the campaign against ISIS, as part of the agreement signed by the U.S. and Turkey on Feb. 17 to allow up to 1,000 U.S. troops to participate in the training in Turkey. - U.S. anti-ISIS envoy meets with Turkish officials The U.S. envoy for the international anti-ISIS coalition, Brett McGurk, arrived in the Turkish capital Ankara Wednesday to meet with Turkish officials. "In Ankara today meeting with senior Turkish officials to advance our joint cooperation against ISIS terrorists," McGurk tweeted on his official account on Wednesday. U.S. President Barack Obama's Special Envoy for the Global Coalition to Counter ISIS, and Deputy Assistant Secretary for Near Eastern Affairs (Iran and Iraq) had visited northern Iraq previously.