Turkish President Recep Tayyip Erdogan said his military will attack armed Kurdish groups in Syria and Iraq "with tanks and soldiers soon" after days of airstrikes as the US and Russia urge restraint.
His comments came as Turkish artillery kept up bombardment of Kurdish bases and other targets near the Syrian towns of Tal Rifaat and Kobani, two Syrian military sources told Reuters.
"We have been bearing down on terrorists for a few days with our planes, cannons and guns," Mr Erdogan said in a speech in northeastern Turkey.
"God willing, we will root out all of them as soon as possible, together with our tanks, our soldiers.
“We will make those who disturb us on our territory pay.”
He said previously that operations would not be limited to an air campaign and may involve ground forces. Turkey has mounted several major military operations against the Syrian Kurdish YPG militia and ISIS militants in northern Syria in recent years.
Syria's main ally Russia, along with the US — which is allied with Kurdish militias in Syria — have both called for de-escalation.
The Turkish attacks have killed dozens of people, mainly Kurdish militia fighters whom Ankara blames for a bomb attack in Istanbul this month.
The explosion on Istiklal Street, a busy shopping area, killed six people and injured more than 80.
The Kurdistan Workers' Party, or PKK, and the Syrian Democratic Forces, a mainly Kurdish militia backed by the US in Syria, both denied responsibility for the attack.
On Wednesday, a Turkish drone hit a base in north-eastern Syria run jointly by the US coalition and the SDF.
Two SDF fighters were killed in a strike on a base north of Hasaka used for planning and executing joint anti-ISIS operations, AFP reported. There was no immediate comment from the US coalition.
Turkey and allied Syrian militias occupy parts of some northern Syrian provinces, having taken them from Kurdish control.
Russia, a leading ally of the Syrian government — which rejects the Turkish presence in northern Syria — as well as the US, has called for restraint.
“We hope to convince our Turkish colleagues to refrain from resorting to excessive use of force on Syrian territory” to “avoid the escalation of tensions”, Alexander Lavrentyev, Russian President Vladimir Putin's special envoy on Syria, told reporters in Astana, Kazakhstan, where an “Astana format” meeting on Syria begins on Tuesday.
The US on Monday evening issued a statement calling for an immediate de-escalation and work to refocus efforts against ISIS, which is active in parts of Syria.
Turkey has launched three major ground offensives in Syria since 2016, working with thousands of allied Islamist militias that Ankara has trained and funded, raising tensions with Washington.
Since 2014, the US and a number of European allies have supported the SDF in the struggle against ISIS.
Mr Erdogan said, “70 planes and drones” that “penetrated 140 kilometres into northern Iraq and 20km into northern Syria” were used in the weekend strikes.
The impetus to launch a ground offensive became stronger on Monday, when rockets fired by Kurdish groups struck civilian buildings in the Turkish border town of Karkamis, killing three people, including a child.
An unspecified number of Syrian soldiers also died in the air strikes, prompting fears that Turkish and Syrian forces could clash, something that happened in 2018. In total, the Syrian Observatory for Human Rights, a UK-based war monitor, said more than 40 people died in the weekend violence.
Mr Erdogan has long stressed the importance of controlling a strip of land along Turkey's southern border, occupying parts of several Syrian governorates since 2016 in an effort to push back Kurdish militias.
“Competent authorities, our defence ministry and chief of staff will together decide the level of force that should be used by our ground forces,” Mr Erdogan said.
Ankara said the Kurdish bases were being used to launch “terrorist” attacks on Turkish soil.
On Monday, thousands gathered to bury 11 people who were killed in Al Malikiyah in Syria's far north-east, including a journalist working for a Kurdish news agency.
“We urge the world, all those who care about human rights and the great powers” to press Turkey to stop its strikes that “target us with planes and drones”, a mourner named Shaaban, 58, told AFP during the funerals.
The US and Germany condemned the latest Turkish offensive, with Washington urging “de-escalation in Syria to protect civilian life and support the common goal of defeating ISIS,” State Department spokesman Ned Price said.
“We continue to oppose any uncoordinated military action in Iraq that violates Iraq's sovereignty.”
Turkey accuses the US of supporting Kurdish terrorist groups. Although the PKK is designated as a terrorist organisation by the US and Europe, Washington insists its SDF allies have no link to the PKK, which has carried out scores of attacks in civilian areas in Turkey.
In Berlin, the German Foreign Ministry also urged Turkey to “react proportionally and to respect international law”, adding that “civilians at all times must be protected”.
Mr Erdogan said he had held “no discussion” with either US President Joe Biden or Russian President Vladimir Putin “on the subject of the operation”.