US Secretary of Defense James Mattis pledged support to Turkey in its ongoing fight against rebels of the Kurdistan Workers Party (PKK) during talks with the country’s president, Recep Tayyip Erdogan, Turkish and US officials said today.

The daylong visit was intended to help smooth fraught relations between the two NATO allies. The biggest thorn is the United States’ partnership against the Islamic State with the PKK’s Syrian franchise, the People’s Protection Units (YPG). Erdogan expressed anger over that alliance to Mattis during a half-hour meeting at the presidential complex. Mattis, in turn, repeated assurances that the US partnership with the YPG is solely tactical and confined to the campaign against IS.

Sources familiar with the substance of the talks confirmed reports in the Turkish media that Mattis had also discussed assisting Turkey against PKK militants based in the Qandil Mountains on the Iraq-Iran border and in the mainly Yazidi-populated Sinjar region on the Iraq-Syria border. The sources told Al-Monitor on condition of anonymity that US support would be “mainly on the intelligence and targeting side.” They dismissed claims by the Turkish press that US troops would carry out a joint ground offensive against the PKK in Sinjar. The Kurdistan Regional Government, a top US and Turkish ally, would also welcome US action to uproot the PKK from Sinjar.

The United States has been sharing intelligence on the PKK since the 1990s, long before the campaign against IS started. The CIA played a critical role in the capture of PKK leader Abdullah Ocalan by Turkish special forces in 1999.