A Kurdish-led force backed by a US-led coalition suspended operations against ISIS and said they would not resume until Turkey halts its attacks on Kurdish militia posts in northern Syria.
The Syrian Democratic Forces, joint Arab-Kurdish units under Kurdish command, announced a "temporary halt" to their operation, launched in eastern Syria on September 10, and condemned Turkey's "provocations".
On Wednesday, Turkish shelling of Kurdish positions in the Kobane sector of northern Syria killed four fighters, according to Turkey's state-run Anadolu news agency.
The SDF condemned what it called the "coordination" of Turkey's attacks with a fightback by extremists and warned of "a prolonged halt to our military operation" against ISIS if Ankara keeps up its strikes.
The US State Department said it had been in touch with both Turkey and the SDF to push for de-escalation.
"Unilateral military strikes into northwest Syria by any party, particularly as American personnel may be present or in the vicinity, are of great concern to us," State Department spokesman Robert Palladino told reporters on Wednesday.
"Coordination and consultation between the United States and Turkey on issues of security concern is a better approach."
Hundreds of Kurdish civilians, carrying party flags and portraits of jailed Turkish Kurdish separatist leader Abdullah Ocalan, demonstrated in the streets of the northeastern city of Qamishli to denounce the Turkish attacks.
"These attacks serve to support the mercenaries" of ISIS, said a protester, 44-year-old teacher Rizan Hamo. "The international community and the world must stop the Turkish state."
Backed by coalition air strikes, the SDF aims to expel ISIS from a holdout on the Iraqi border, but the extremist group staged a fierce fightback last week under the cover of a sand storm, using suicide bombings to force a retreat.
According to the Syrian Observatory for Human Rights, the ISIS counter-attack killed at least 72 fighters from the SDF, which is dominated by the Kurdish People's Protection Units (YPG).
The monitoring group said hundreds of Kurdish fighters, men and women, had since been deployed on the outskirts of the ISIS holdout of Hajin.
But, the Britain-based monitor said on Wednesday, "on the ground, everything has come to a halt".
On Tuesday, two days after another round of shelling of Kurdish posts in northern Syria, Turkey's President Recep Tayyip Erdogan said his country had completed preparations for a new operation to "destroy" the YPG militia, which Ankara has branded a terrorist group.
"We are going to destroy the terrorist structure in the east of the Euphrates. We have completed our preparations, plans, programmes regarding this issue," said Mr Erdogan, who has made similar threats in the past.
The YPG has worked closely with the United States in the fight against ISIS in Syria, straining ties between NATO allies Washington and Ankara.
The animosity between Syria's Kurds and Turkey underlines the complexity of the multi-front Syrian conflict that has cost over 360,000 lives since it broke out in 2011 with anti-government protests that were violently suppressed by the regime.
Earlier this year, Turkish military forces supported Syrian opposition fighters in seizing the Afrin region, west of the Euphrates, from the YPG in a two-month air and ground offensive.
Ankara previously launched an offensive between 2016 and 2017 against ISIS on its border with Syria, as well as blocking the YPG from linking up areas under its control.