Turkey's prime minister said on January 20 that Turkish air strikes had begun against an enclave controlled by U.S.-backed Kurdish fighters in northwestern Syria.
Prime Minister Binali Yildirim's comments followed a statement earlier in the day by Turkish President Recep Tayyip Erdogan that a military operation had begun in the enclave, Afrin, and that another operation in nearby Manbij would follow.
"As of this moment, our brave armed forces have started the aerial offensive to eliminate elements" of the Kurdish People's Protection Units (YPG) militia in Syria and Islamic State (IS) militants, Yildirim said in a televised speech.
Turkey's military said the offensive, code-named Operation Olive Branch, had been launched at 5 p.m. local time and was part of Ankara’s right to self-defense.
The Associated Press cited a spokesman for the Syrian Kurdish militia group as confirming that the enclave was being targeted in Turkish aerial bombardments.
Ankara considers the YPG to be a terrorist organization and is angry that Washington is allied with the Kurdish YPG forces that have been fighting against IS militants in Syria.
The United States had urged Turkey not to launch such an operation, saying the focus should remain on battling IS.
The Russian Foreign Ministry on January 20 voiced concern about the new offensive and called on "the opposing parties to show restraint."
The Russian Defense Ministry, meanwhile, said in a statement that it was withdrawing its troops from the area in order "to prevent potential provocation and exclude the threat to the life and well-being of Russian military."
Russia has given Syrian President Bashar al-Assad's government crucial military backing throughout the war, which has killed hundreds of thousands of people and displaced millions since it began with a state crackdown on pro-democracy protesters in March 2011.
Turkey's government was infuriated by a January 14 statement from the U.S.-led coalition in Syria that said Washington would help set up a new 30,000-strong border force in Syria that includes the YPG.
U.S. Secretary of State Rex Tillerson says he told Turkish Foreign Minister Mevlut Cavusoglu on January 17 that the "entire situation has been misportrayed” and "misdescribed" by "some people" who "misspoke."
Tillerson said the United States aims to provide training to local elements in Syria, not create a new border security force.