U.S. Secretary of Defense James Mattis is in Ankara today amid discussions on Turkey's military operation against the Syrian town of Afrin held by the PKK-affiliated Democratic Union Party's (PYD) People's Protection Units (YPG) militia and increased possibilities of a joint Turkish-Iranian operation against the PKK.

Today in Ankara, Mattis will meet with National Defense Minister Nurettin Canikli. He will then meet with President Recep Tayyip Erdoğan. According to diplomatic sources, the ongoing fight against Daesh, the Kurdistan Regional Government's (KRG) upcoming independence referendum and Turkey's concern about the PYD and YPG are expected to be the main issues discussed.

Mattis visited Iraq's capital of Baghdad where he met Iraqi Prime Minister Haider al-Abadi on Tuesday before than arriving in Ankara. He later went to Irbil and met with KRG President Masoud Barzani. An Iraqi readout said in Baghdad Mattis and Iraqi officials discussed enhancing joint military cooperation. In Irbil he reportedly asked Barzani to postpone the independence referendum that will take place in Sep. 25.

Mattis's visit comes after Iranian Chief of Staff Gen. Mohammad Hossein Bagheri visited Ankara last week where he discussed with Turkish officials a joint operation against the PKK affiliate in Iran, the Kurdistan Free Life Party (PJAK), and the situation in Syria.

Ankara considers the YPG to be a national threat and they are concerned about U.S. arms support to the YPG. In order to ease Ankara's strong objection Mattis sent a letter to Chief of General Staff Gen. Hulusi Akar in June as part of a mechanism to inform Ankara about the weapons the U.S. provides to the YPG.

"Secretary Mattis will emphasize the steadfast commitment of the United States to Turkey as a NATO ally and strategic partner, seek to collaborate on efforts to advance regional stability, and look for ways to help Turkey address its legitimate security concerns - including the fight against the PKK," the Pentagon said in a statement on the visit.