"The administration's decision to arm the Syrian Democratic Forces, which are predominantly Kurdish, makes military sense, but will aggravate Turkey", Phillips said.
Earlier, Turkish Foreign Minister Mevlut Cavusoglu also denounced the US move, saying "every weapon that reaches the (Kurds') hands is a threat to Turkey".
Erdogan also called on the United States to stand alongside a North Atlantic Treaty Organisation ally - Turkey - and reverse its decision on arming Syrian Kurds before his upcoming visit to Washington.
The YPG militia is a key component of the Syrian Democratic Forces (SDF), the coalition partners of the US on the ground in Syria fighting Islamic State extremists.
Washington's decision to support the YPG will also likely preclude any repeat of last month's Turkish military strikes against the Syrian Kurdish militia, both in Syria and Iraq.
But this sparked ire from Turkey, which regards the YPG as the Syrian branch of the Kurdistan Workers Party (PKK), which since 1984 has waged an insurgency inside Turkey, leaving tens of thousands dead.
Turkish President Tayyip Erdogan, who will meet U.S. President Donald Trump in Washington next week, has voiced hopes Washington might reverse the decision.
"We'll work out any of the concerns", U.S. Defense Secretary Jim Mattis said Wednesday. The spokesman for the USA -led coalition against IS, Col. John Dorrian, said US troops were about 6 miles from the strikes and put American forces at risk.
Khalil dismissed the label, saying the US would not supply arms to terrorists.
The YPG said Washington's decision would bring swift results and help the militia "play a stronger, more influential and more decisive role in combating terrorism".
Coalition spokesman Col. John Dorrian said the capture of Tabqa is "yet another victory" for the Kurdish-led forces, the U.S.'s most effective partner on the ground in Syria fighting IS.
Before his meeting with Mattis, Yildirim had warned that "there is still an opportunity for the United States to take Turkey's sensitivities into consideration". In a brief readout of the approximately 30-minute meeting held ahead of the start of a Somalia conference, a Pentagon statement said the two men discussed a range of bilateral security issues.
The green light was given just one week before Turkey's president will visit the White House.
"We'll work out any of the concerns".
The Syrian Kurds have been encircling Raqqa, preparing for the launch of what the USA military predicts will be a long and hard battle to retake the city. Russia-the key ally of Syrian President Bashar al-Assad-and Turkey have been on opposite sides of the Syrian conflict but are working increasingly closely together in search of peace.
A Turkish air raid in late April killed 20 YPG fighters and media officials, prompting the U.S. to deploy armoured vehicles along the border in a show of support for the group.