Turkey has said it is planning a ground operation against the Syrian Kurdish People’s Protection Units (YPG), after four days of strikes in Syria and Iraq.
President Recep Tayyip Erdogan warned that the strikes – which his defence minister claimed had “neutralised” 254 terrorists – were “only the beginning”.
Turkey has blamed Kurdish groups for a recent deadly bomb attack in Istanbul.
The YPG has denied involvement and said the strikes in north-east Syria have killed 30 civilians and 11 fighters.
The US defence department said the Turkish attacks had “directly threatened the safety of US personnel” working in Syria to defeat jihadist group Islamic State (IS).
The Syrian Democratic Forces (SDF), a US-backed militia alliance dominated by the YPG, has accused Turkey of using the Istanbul bombing as a pretext to launch a long-planned cross-border offensive.
The Turkish military has launched three large-scale operations with allied Syrian rebel groups in northern Syria since 2016 and currently controls a swathe of territory running along more than 325km (200 miles) of the border.
The most recent operation, in 2019, saw Turkey capture the area between the towns of Tal Abyad and Ras al-Ain before Russia brokered a ceasefire.
Turkey considers the YPG a terrorist group, insisting that it is an extension of the Kurdistan Workers’ Party (PKK), which has fought for Kurdish autonomy in Turkey for decades. The PKK has also denied involvement in the Istanbul bombing, which killed six people in the city’s central Istiklal Avenue on 13 November.
In a speech to members of his AK Party in parliament on Thursday, President Erdogan said Turkey’s determination to secure its border with Syria and establish a “security corridor” was “stronger than ever before”.
“We are continuing the air operation and will come down hard on the terrorists from land at the most convenient time for us,” he warned.
SDF commander Mazloum Abdi told Al-Monitor that he believed his home town of Kobane would be the true target of any ground assault and alleged that the Istanbul attack was “perpetrated by Syrian opposition groups operating under Turkey’s control”.
Mr Abdi also said Russia and the US were not doing enough to deter Turkey.
Russia, an ally of the Syrian government, has warned Turkey that a full-scale ground offensive could trigger an escalation of violence.
“We hope our arguments will be heard in Ankara and other ways of resolving the problem will be found,” Russian negotiator Alexander Lavrentyev said on Wednesday following talks in Kazakhstan.
The US, a Nato ally of Turkey, warned about the impact any escalation could have on the goal of fighting Islamic State. The US relied on the YPG and other militias in the SDF to defeat IS in eastern Syria.
The SDF said on Wednesday that five Turkish air strikes had targeted Kurdish security forces guarding the al-Hol detention camp, where the relatives of suspected IS militants are being held.
The US military meanwhile said that a Turkish drone strike against Mazloum Abdi’s main headquarters north of the city of Hassakeh on Tuesday had put US troops in danger. The SDF said the strike killed two of its fighters.