Turkey says it has suffered its deadliest day yet in northern Syria since launching its offensive against YPG Kurdish fighters there more than two weeks ago.
On Saturday, eight Turkish soldiers were killed, according to a Turkish army statement.
Some died after their tank came under fire from Syrian Kurdish forces.
Turkey wants to push the YPG, which it says are "terrorists", out of Afrin to create a buffer zone along its southern border.
YPG fighters targeted the Turkish army tank in Sheikh Haruz, northeast of Afrin, killing five soldiers. Three other soldiers were killed in fighting elsewhere in Afrin.
Turkish Prime Minister Binali Yildirim promised to retaliate in a statement on Twitter.
"They will pay for this twice as much. We have given the necessary response instantly, and we continue to do so," Yildirim said.
Immediately after the attack at Sheikh Haruz, an air operation targeting YPG positions and weapon storages in the area was launched, the army said.
Turkey's Operation Olive Branch began on January 20 along with the Free Syrian Army (FSA) to clear armed Kurdish groups and Islamic State of Iraq and the Levant (ISIL, also known as ISIS) fighters from Afrin in northwestern Syria.
Since the start of the operation, Kurdish fighters have carried out cross-border attacks by firing rockets into southern Turkey.
According to the Turkish army, the operation aims to establish security and stability along Turkish borders and the region as well as to protect Syrians from what Ankara called "terrorist oppression and cruelty".
Meanwhile, Syrian rebels shot down a Russian warplane in northwestern Idlib province on Saturday, the Russian defence ministry said.
The pilot of the aircraft, a Sukhoi 25, used his ejection seat after his plane was hit by a man-carried portable air defence missile.
He was later killed when rebels tried to capture him.
"The pilot managed to report the ejection in the area controlled by the militants of Jabhat al-Nusra, but later he died fighting the terrorists," a statement by the Russian ministry of defence said.
The downing of the aircraft has been claimed by Hay'et Tahrir al-Sham, commonly known as Tahrir al-Sham. The group is spearheaded by the former al-Nusra Front, which used to be al-Qaeda's branch in Syria.
Moscow has retaliated with dozens of attacks in which at least 10 civilians were killed, according to local activists. Russia says it has killed 30 fighters.
There has been heavy fighting in Idlib for weeks. The UN says about 100,000 civilians have been displaced.