The SDF has not given a casualty toll, while six fighters with Turkey-backed rebel groups have also been killed
Turkey pressed its military offensive against US-allied Kurdish fighters in northeast Syria on Thursday, shelling towns and bombing targets from the air in an operation that has forced thousands of people to flee their homes.
At least 23 fighters with the Kurdish-led Syrian Democratic Forces (SDF) and eight civilians, two them SDF administrators, have been killed, the Syrian Observatory for Human Rights said.
The SDF has not given a casualty toll, while six fighters with Turkey-backed rebel groups have also been killed.
More than 60,000 people have fled since the offensive began, the Observatory added. The towns of Ras al-Ain and Darbasiya, some 60 km to the east, have been largely deserted as a result of the attack.
Turkish President Tayyip Erdogan told members of his AK Party in Ankara that 109 militants had been killed so far in the two days of fighting, while Kurds said they were resisting the assault.
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," Erdogan said in a speech to members of his AK Party in Ankara.
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 US forces from the border, and senior members of US President Donald Trump's own Republican Party condemned him for making way for the incursion.
The decision has been widely criticised 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 US officials, credit the Kurds with fighting alongside American troops to defeat Islamic State militants.
The Kurdish-led authority in northern Syria said a prison struck by Turkish shelling holds "the most dangerous criminals from more than 60 nationalities" and Turkey's attacks on its prisons risked "a catastrophe". [nS8N1XQ025]
The Kurdish-led Syrian Democratic Forces (SDF) holds thousands of Islamic State fighters and tens of thousands of their relatives in detention.
There was no immediate comment on the situation in the prisons from Turkey.
Trump called the Turkish assault a "bad idea" and said he did not endorse it. He said he expected Turkey to protect civilians and religious minorities and prevent a humanitarian crisis - as Turkey has said it would.
Republican Senator Lindsey Graham, usually a vocal Trump ally, has criticized his decision to withdraw US troops from northeastern Syria and unveiled a framework for sanctions on Turkey with Democratic Senator Chris Van Hollen.
Their proposed sanctions would target the assets of senior officials including Erdogan, mandate sanctions over Turkey's purchase of a Russian S-400 missile defence system and impose visa restrictions.
They also would sanction anyone who conducted military transactions with Turkey or supported energy production for use by its armed forces, bar US military assistance to Turkey and require a report on Erdogan's net worth and assets.
The United Nations Security Council will meet on Thursday to discuss Syria at the request of the five European members, Britain, France, Germany, Belgium and Poland.
In a letter to the 15-member Council seen by Reuters, Turkey said its military operation would be "proportionate, measured and responsible".
The 22-member Arab League said it would hold an emergency meeting on Saturday.
Israeli Prime Minister Benjamin Netanyahu condemned Turkey's military incursion and cautioned about the possibility of ethnic cleansing.
"Israel is prepared to extend humanitarian assistance to the gallant Kurdish people," he wrote on Twitter.
Russia said it planned to push for dialogue between the Syrian and Turkish governments following the incursion.
Italy condemned the offensive as "unacceptable", saying military action in the past always led to terrorism.
"The intervention risks greater humanitarian suffering and undermines the focus on countering Daesh (IS)," said British Foreign Secretary Dominic Raab.