According to a senior Turkish security official, armed forces struck weapons and ammunition depots, gun and sniper positions, tunnels and military bases.
Jets conducted operations up to 30 km (18 miles) into Syria, and a Reuters witness saw shells exploding just outside the town of Tel Abyad.
“The operation is currently continuing with the involvement of all our units... 109 terrorists have been killed so far,” President Tayyip Erdogan said in a speech to members of his AK Party in Ankara.
Thousands of people have fled Ras al Ain towards Hasaka province since the operation began. The Turkish air strikes killed at least five civilians and three fighters from the SDF and wounded dozens of civilians, the SDF has said.
NATO member Turkey has said it intends to create a “safe zone” for the return of millions of refugees to Syria.
But world powers fear the operation could intensify Syria’s eight-year-old conflict, and runs the risk of Islamic State prisoners escaping from camps amid the chaos.
Erdogan sought to assuage those concerns, saying that militants from the jihadist group would not be allowed to rebuild a presence in the region.
Taking aim at the European Union and Arab powers Saudi Arabia and Egypt, which have voiced opposition to the operation, Erdogan said those objecting to Turkey’s actions were dishonest.
He threatened to permit Syrian refugees in Turkey to move to Europe if EU countries described his forces’ move as an occupation. Turkey is hosting around 3.6 million people who have fled the conflict in Syria.
“They are not honest, they just make up words,” Erdogan said in a combative speech, singling out Saudi Arabia and Egypt. “We, however, take action and that is the difference between us.”
The Turkish operation began days after a pullback by U.S. forces from the border, and senior members of U.S. President Donald Trump’s own Republican Party condemned him for making way for the incursion.
The decision has been widely criticized as an abandonment of Syrian Kurds.
Ankara brands the Syrian Kurdish YPG militia as terrorists because of their ties to militants who have waged an insurgency in Turkey. But many members of Congress, and U.S. officials, credit the Kurds with fighting alongside American troops to defeat Islamic State militants.
“Our heroic commandos taking part in Operation Peace Spring are continuing to advance east of the Euphrates (river),” the Turkish Defense Ministry wrote on Twitter. “The designated targets were seized,” it said in a later statement.