The United States has urged Turkey and Kurdish forces in Syria to quit firing at each other as reports of fresh violence between the two parties threaten their efforts to counter Islamic State.
"We are concerned about the situation north of Aleppo and are working to de-escalate tensions on all sides," a Pentagon statement said.
"We have urged Syrian Kurdish forces affiliated with the YPG not to take advantage of a confused situation by seizing new territory. We have also seen reports of artillery fire from the Turkish side of the border and urged Turkey to cease such fires."
The Pentagon noted that the Turkish and Syrian Kurdish forces share an enemy in Islamic State, and urged all parties to abide by agreements made in Munich last week to seek a cessation of hostilities in Syria.
The State Department issued an identical statement on Saturday from spokesman John Kirby.
The French Foreign Ministry on Sunday also called for Turkey to halt bombardments.
"France is worried about the deteriorating situation in the region of Aleppo and the north of Syria," it said in a statement.
"We call for the cessation of all bombardments, those of the regime and its allies on the entire territory and those of Turkey in the Kurdish zones."
Turkish President Recep Tayyip Erdogan has criticised the US for backing the YPG, Syrian Kurdish fighters who are classified by Turkey as terrorists.
Earlier this month, Brett McGurk, President Barack Obama's envoy for the international coalition against Islamic State, visited the Syrian town of Kobani, where Kurds fought back a siege by Islamic State near Turkey's border last year.
Turkish Prime Minister Ahmet Davutoglu was reported earlier on Saturday as saying that Turkey had returned YPG shellfire from the Syrian town of Azaz under the military's rules of engagement, according to the state-run Anadolu news agency.
Mr Davutoglu said the latest developments in Syria threatened Turkey's national security, and he told Kurdish YPG militants to pull back immediately from areas surrounding Azaz.
Mr Davutoglu said he had informed US Vice-President Joe Biden in a phone call that Turkey would take all necessary measures to respond to the threat.
Anadolu also reported on Saturday that Turkish forces responded to a mortar attack from the Syrian military that targeted a police station in Turkey, citing an unidentified military source who didn't disclose what form of retaliation Turkey used.
Turkey's disquiet has been heightened by the tens of thousands of people fleeing to the Turkish border after attacks by Russian-backed Syrian government forces, swelling refugee numbers in the area to 100,000.
Turkey, which already hosts 2.6 million Syrian refugees, has kept the latest arrivals on the Syrian side of the border, in part to pressure Russia to cease its air support for Syrian government forces near the city of Aleppo.
Mr Davutoglu earlier condemned the attacks in Aleppo as "barbarity, tyranny, a war strategy conducted with a medieval mentality" and said hundreds of thousands faced the danger of starvation if a humanitarian corridor was not opened.
"We will help our brothers in Aleppo with all means at our disposal. We will take those in need but we will never allow Aleppo to be emptied through an ethnic massacre," he said.
NATO-member Turkey is one of Syrian President Bashar al-Assad's most vehement critics and an ardent supporter of opposition forces.
Turkish Foreign Minister Mevlut Cavusoglu was reported as saying on Saturday that Saudi Arabia would send aircraft to Turkey's Incirlik air base for the fight against Islamic State.