Turkish defense ministry sources said US Defense Secretary Jim Mattis also promised his Turkish counterpart to provide a monthly list of weapons handed to the YPG, saying the first inventory had already been sent to Ankara.
Turkey sees the YPG as an extension of the outlawed Kurdish PKK, which has been waging an insurgency in the country's southeast since the mid-1980s. It has said supplies to the YPG have in the past ended up in PKK hands, and described any weapon given to the force as a threat to its security.
The United States sees the YPG as an essential ally in the campaign to defeat Islamic State in Raqqa, the jihadists' main urban base in Syria. The fight for Raqqa was launched two weeks ago, piling pressure on Islamic State which also faces defeat in its Iraqi stronghold of Mosul.
Mattis told Turkish Defence Minister Fikri Isik that a detailed record of all equipment provided to the YPG was being kept and that all the weapons would be taken back after Islamic State was defeated, the sources said.