Kurdish-backed fighters in Syria say they will not withdraw from the areas they have recently captured in the country's north, after Turkey shelled their positions in Aleppo province for a second day.
Turkey has demanded that the People's Protection Units (YPG), the armed wing of Syria's Kurdish Democratic Union Party (PYD), give up the territories it has gained in the past few days from Turkish-backed Syrian armed groups.
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Speaking to Al Jazeera from Afrin on Sunday, Tarek Abu Zeid, a spokesman of Jaish al-Thuwar, a YPG ally, said: "We recently captured Menagh air base, and we are close to capturing Tal Rifaat."
Referring to the Islamic State of the Iraq and Levant group, he said: "Our aim is to reach ISIL-controlled territories.
"We want to fight this terrorist group. Turkey wants us to return to Afrin. This won't happen. We are advancing, we won't retreat."
'Stabbed in the back'
A Turkish government official told Al Jazeera on Sunday that the army was continuing to target positions of the YPG and its allies in northern Syria.
The Syrian Observatory for Human Rights, a UK-based monitoring group, also reported the artillery bombardment, saying that two fighters died on Sunday.
Turkey has been warning the Kurdish fighters, which it sees as "terrorists", not to expand their positions since the beginning of the conflict in 2011.
|Positions as of January 2016 [Al Jazeera]
The YPG is in control of almost all of Syrian-Turkish border and, in recent days, the group and its allies have expanded their territorial gains by taking advantage of a major Russia-backed government offensive in Aleppo.
The advances by both the Syrian government and the YPG are putting pressure on the opposition.
"We are being stabbed in the back in the northern countryside by the PKK and its ally Jaish al-Thawar," said Mudar Najjar, a commander for the Free Syria Army.
"They took advantage of the fact that we were fighting on two fronts - against the regime and ISIL."
The U.S. sees the PYD as a close ally in the campaign against ISIL in Syria.
But Turkey believes that the PYD is the Syrian wing of the Kurdistan Workers' Party (PKK), which has been locked in battle with Turkish forces for more than 30 years.
The PKK is seen as a "terrorist organisation" by the U.S. and Europena Union, while the PYD is not.
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"The PYD is trying to carry out an ethnic cleansing by raiding areas where there is no or little Kurdish population and works to remove non-Kurdish ethnic elements out of these areas," Yasin Aktay, a Turkish government MP, told Al Jazeera.
Al Jazeera's Zeina Khodr, reporting from the Turkish town of Gaziantep near the Syria border, said Turkey's latest actions send a clear message that it will stand by its red lines.
"Turkey's policy in Syria has been clear from the beginning," she said.
"It wants regime change in Syria and it wants to prevent a Kurdish state from being created along its borders. It believes a safe zone along the Syrian side of the border could serve as a buffer to protect its interests - a demand so far not accepted by the international community."
On Sunday, Syria's government condemned Turkey's shelling and called the UN to act, state media said.
"The foreign ministry strongly condemns the repeated Turkish crimes and attacks against the Syrian people and Syria's territorial integrity," state news agency SANA reported.
Source: Al Jazeera and agencies