Turkey shelled US-backed Kurds in northern Syria on Sunday for the second successive day despite a call for a halt from Washington, a monitoring group said.
The Syrian Observatory for Human Rights added that Turkish forces shelled positions held by the Kurd-led Democratic Forces of Syria (DFS), a coalition linked to the powerful Kurdish People's Protection Units (YPG) in the northern and north-western parts of the embattled Aleppo province.
At least two DFS fighters have been killed and seven injured in the shelling over the past 24 hours, according to the Britain-based watchdog.
The shelling targeted a strategic airbase and other posts that the Kurds had captured earlier this week from Islamist rebels near the Turkish border.
On Saturday, Turkey vowed to continue the attack and demanded the Kurds withdraw from the areas.
The United States, an ally of Turkey, called on Ankara to stop the shelling and focus on fighting the Islamic State extremist militia that rules territory in Syria.
The Syrian Kurdish insurgents are the main US ally on the ground against Islamic State, but they are also closely linked to banned Kurdistan Workers' Party (PKK) rebels fighting inside Turkey.
The ongoing violence comes amid increasing doubts on the chances for the implementation of a partial ceasefire in Syria agreed by major powers, including the US and Russia, on Friday in Munich.
Forces of Syrian President Bashar al-Assad, backed by Russian airstrikes, pressed ahead Sunday with a major attack against the rebel-held towns of Anadan and Hreitan on the northern outskirts of Aleppo, according to activists. No casualties were reported.
Al-Assad's forces, with a Russian air cover, have made significant territorial gains in the area since they started their onslaught earlier this month.