In a joint press conference with Sierra Leone President Ernest Bai Koroma,Erdogan said: "Every development in Syria and Iraq is a matter of national security for us [Turkey].
"We would like to believe that our allies will prefer to side with us and not with terrorist organizations," Erdogan added.
On Tuesday, the Pentagon announced that U.S. President Donald Trump had approved arming "Kurdish elements" of the Syrian Democratic Forces (SDF) ahead of an attempt to drive Daesh from Raqqah, the last Syrian city held by the terror group.
The SDF is spearheaded by the PKK/PYD and its armed wing, the PKK/YPG. Turkey views both as Syrian affiliates of the PKK terror group that has fought a 33-year war against the state and is also listed as a terror organization by the U.S. and EU.
The U.S. has, however, used the PKK/PYD as its ally in Syria to help combat Daesh despite repeatedly demands by Ankara for Washington to end its ties to the PKK/PYD. Turkey has also offered to help take Raqqah.
Erdogan said he would express his concerns during a meeting with Trump in Washington on May 16, adding that the issue would also be addressed May 25 at a NATO summit in Brussels.
"I believe that these meetings will ensure the stability of the region and will lead us to reach a conclusion compatible with the realities of Syria.”
Erdogan also said he hoped the U.S. government would "reverse" its decision to arm the PKK/PYD in Syria "before I go to America".
The president reiterated that the fight against Daesh terrorist organization "should not be carried out with the help of another terrorist organization”.
Seeking to allay Turkish concerns, U.S.-led anti-Daesh coalition spokesman told reporters in Washington the coalition will make sure the weapons that will be provided "are pointed at ISIS".
He was using another acronym for Daesh.
"We're going to carefully monitor what's being provided and what it's used for, and we are completely committed to make sure that its being used for exactly the purpose that we intend," Air Force Col. John Dorrian said via video link from Baghdad, Iraq.
The arms, which will be "distributed soon", will include small arms, ammunition, heavy machine guns and other weapons to eliminate Daesh's vehicle-borne bombs, Dorrian said.
Asked if the last category would include anti-tank TOW missiles, Dorrian said it would include "other capabilities that can address that level of threat".
Dorrian stressed that the coalition "very much" values Turkey's security.
"ISIS threatens them, as has the PKK, which the U.S. has recognized as a terrorist organization for right about 20 years now," he said. "So, we're going to stay focused on working with them to defeat ISIS."