Turkey: Between old alliances and Kurdish anger
Turkish tanks have amassed near the border with Syria, while Turkish media reported that medical personnel in Kilis, a Turkish town across the border from Afrin, were asked not to take leave, apparently in anticipation of military operations.
On Wednesday, Ankara warned it has no qualms about taking action in Syria's Afrin district should the United States insist on backing a Kurdish-led force there.
The US-led coalition fighting the Islamic State group said last week that they were working with the Syrian Democratic Forces (SDF) to create a 30,000-strong border security force in northern Syria, a statement that drew sharp condemnation from other countries.
The coalition added that the force is a key element of its strategy to prevent the resurgence of the Islamic State group in Syria and would be deployed along Syria's border with Turkey and Iraq.
However, Washington has since backtracked and denied such plans, saying "some people misspoke." Rex Tillerson, the US Secretary of State refuted any intention of building the force, saying the issue had been "misportrayed, misdescribed".
"Some people misspoke. We are not creating a border security force at all," Tillerson told reporters.
"I think it's unfortunate that comments made by some left that impression," he said, without giving details. "That is not what we're doing."
Ankara is fiercely opposed to the SDF, which is dominated by the Kurdish People's Protection Units (YPG) – considered by the Turkish government to be a "terrorist" group.
Turkey views the YPG as an extension of PKK, the Kurdistan Workers' Party, and described the force as a "terror army". The PKK is considered a terrorist group by the European Union, Turkey and the United States.
Iran also joined Turkey in hitting out at the proposed plans, saying that it will only cause more instability and "add flames of fire" in an already war-torn country.
Syrian President Bashar al-Assad responded by vowing to crush the new "traitor" force and drive US troops from Syria, and powerful ally Russia called the plans a plot to dismember Syria and place part of it under US control.
Erdogan has long threatened an operation against the YPG's enclave in Afrin but has stepped up his threats in recent days, saying Ankara troops will clear it of "terrorists".
On Tuesday, he warned an assault on Afrin could take place "tomorrow, (or) the day after, (or) within a short period".
Turkey's defence minister, Nurettin Canikli, said on Friday there was no turning back from launching a ground assault on Syria's Afrin enclave, saying the offensive had "de facto" started with sporadic Turkish military shelling of the area.
As Turkey sends troops and tanks to the border, the operation threatens to spill into a wider Turkish-Kurdish confrontation inside the country. The Afrin district houses no less than 800,000 civilians, including displaced people from earlier years of the Syrian war, and there are concerns that it could turn into a humanitarian disaster.
"Turkey remains a loyal and trusted friend and ally of the US and the West. But that does not mean we will accept being treated as sacrificial animals just because a couple of American generals want to embark on an adventure in the Middle East," Ilnur Cevik, an Erdogan presidential adviser, wrote in the Turkish daily Sabah.
Despite the US assurances, there doesn't appear to be a major shift in their Syria policy.
"If anything, he exacerbated it. Erdogan will perceive Tillerson's announcement of longer term US presence in Syria as doubling down on our partnership with (the Kurdish militia), which does not de-escalate the Turks," said Elizabeth Teoman to AP, a Turkey researcher with the Washington-based Institute for the Study of War.
The Trump administration has been urging Turkey not to attack Afrin, asking Turkish officials to avoid unilateral actions.
Several thousand people took to the streets on Thursday in Kurdish-held parts of northern Syria in protest against Erdogan.
"We are united and we want to support our people in Afrin," said Abdallah Khaled, a 40-year-old protester to AFP, in the northeastern province of Hassakeh.
Protesters shouted "Down, down, Erdogan!" and "With our soul, with our blood, we are with you Afrin!"
Some waved Kurdish and YPG flags while others carried portraits of Abdullah Ocalan, imprisoned leader of the PKK.
Signs in Arabic and Kurdish read: "We condemn the attack by the Turkish state against our people in Afrin."
Several other parts of Kurdish-controlled territories saw similar gatherings, notably Afrin itself, where organisers said tens of thousands of people took to the streets despite the rain.
In response to Erdogan's threats, Kurdish fighters have said that their forces are ready to fight the Turkish army, with the commander of a powerful militia force saying he will not be intimidated by Turkey threats to target in Afrin and Manbij.
"We will foil Erdogan's filthy plans. We will turn those plans to major victories for the people of the region, the Kurdish, Syrian, and Turkish people," YPG chief, Sipan Hemo pledged.Hemo added that his Kurdish fighters would "cleanse" an area in northern Syria it occupies of Ankara's "scourges", reported Kurdish media.