Turkish President Recep Tayyip Erdogan today laid out his agenda for Saturday talks with Vice President Joe Biden, saying a Russian military build-up in northern Syria, which reported involves "up to 200" Russian troops, is threatening to Turkey and "won't be tolerated."

Erdogan expressed particular concern about reports of a team of Russian military engineers arriving in Qamishli, in Hasakeh Province, to investigate the possibility of expanding the runway and capacity of the airport to serve as a Russian air base in northeastern Syria.

The US has recently taken over a base in the same area of Hasakeh from the Kurdish YPG, and Russia seems keen to get a base there as well, as they've similarly backed the YPG against ISIS. Erdogan, however, insisted that "There is no difference between PYD, YPG, PKK, or ISIS."