By Davut Colak, Sarp Ozer and Mumin Altas

ANKARA

Defense Minister Fikri Isik and his U.S. counterpart James Mattis spoke over the phone on Tuesday about the planned military operation in the northern Syrian city of Raqqah.

The two ministers discussed the ongoing crises in Syria and Iraq, according to a Turkish Defense Ministry source, who spoke on condition of anonymity due to restrictions on talking to media.

In a separate meeting on Tuesday in the Danish capital of Copenhagen, Mattis said the U.S. and Turkey would work together as operations to retake Daesh-held Raqqah continue.

The Pentagon chief's remarks came during an anti-Daesh coalition meeting.

"Our intent is to work with the Turks, alongside one another, to take Raqqah down, and we're going to sort it out and we'll figure out how we're going to do it," Mattis said.

About the standoff between the two sides over the U.S. alliance with PKK affiliates PYD/YPG in the fight against Daesh, Mattis said the two countries are NATO allies and have been in useful discussions on the military and diplomacy.

"That's not to say we all walk into the room with exactly the same appreciation of the problem or the path forward," he added.

Turkey has repeatedly called for an end to U.S. support for the PYD/YPG. But while the U.S. classifies the PKK as terrorists, it calls the PYD/YPG its ally in the fight against Daesh in Syria.

The PKK -- listed as a terrorist organization by Turkey, the U.S. and the EU -- resumed its armed campaign against Turkey in July 2015.

Since then, it has been responsible for the deaths of some 1,200 Turkish security personnel and civilians, including a number of women and children.