VILNIUS (AFP) - Pentagon chief Jim Mattis said Wednesday (May 10) he is confident the United States can allay any concerns Turkey has over the decision to arm Syrian Kurdish fighters whom Ankara considers terrorists.

"We will work very closely with Turkey in support of their security on their southern border," Mattis said at a news conference in Lithuania.

"We have very open discussions about options and we will work together, we will work out any of the concerns. I am not concerned at all about the NATO alliance and the relations between our nations." The Pentagon on Tuesday said President Donald Trump had approved arming Kurdish fighters ahead of an eventual offensive to recapture the Islamic State group's Syrian stronghold of Raqa.

The Kurdish Peoples' Protection Units (YPG) is seen by Washington as the best ally against IS in Syria and the prime attacking force in any assault on Raqa.

But Ankara regards the YPG as a terror group and the Syrian branch of the Kurdistan Workers' Party (PKK), which since 1984 has waged an insurgency inside Turkey leaving tens of thousands dead.