Canikli said he told Mattis that US support for the Syrian Kurdish militia, known as YPG, has helped Kurdish rebels in Turkey "to grow and strengthen", posing an increasingly "existential" threat to Turkey.
Tillerson will try to bridge the gap in the relations between the two countries that has grown, mainly on the issue of Syria in which Washington is in every way supporting the forces of the Syrian militia's Kurdish militia (YPG), with Ankara invade Syria to fight them, since they consider them to be terrorists and a branch of the PKK.
Turkey's operation against the YPG, which Ankara blacklists as a terror group, has seen Turkish troops fighting a militia which is closely allied with the U.S. in the battle against Islamic State (IS) group jihadists.
However, the Syrian Army maintains that they will continue to allow the Kurdish forces to resupply the area from within their own territory in Aleppo.
Assad has described US-sponsored Kurdish armed elements as "traitors" to the nation but has also denounced Turkish incursions as an act of aggression.
Tylerson has protested against the Turkish operation in Afrin, stressing that "it is turning the attention of the forces fighting against the jihadists away from their main fight".
Manbij is strategically important to the US-led coalition's goal to contain and defeat ISIS, Tillerson said.
"Turkey is a part of the D-ISIS Coalition, in addition [to] a North Atlantic Treaty Organisation ally, so we continue our operations out of there". We are not talking about Russian soldiers, ' said foreign ministry spokeswoman Maria Zakharova.
"We will work together. we have good mechanisms on how we can achieve this, there is a lot of work to be done", he said. The Turkish government believes YPG to be an extension of the Kurdistan Workers' Party (PKK), outlawed in Turkey as a terrorist organization. Tillerson said priority will be given to the issue of Manbij as the two sides work together.
Speaking in Beirut before his meeting with Erdogan, Tillerson denied Washington ever gave heavy weaponry to the YPG and thus could not gather up such arms, as desired by Ankara.
Cavasoglu said other working groups would tackle the question of the YPG and of Fethullah Gulen, a Turkish cleric who lives in Pennsylvania and who Erdogan's government accuses of plotting a coup.
Compounding the difficulties over Syria, ties had also been damaged by what Ankara perceives to be Washington's reluctance to extradite US -based cleric Fethullah Gulen and the trial in the United States against a banker accused of helping Iran evade sanctions.