Turkey escalated its offensive Thursday against Kurdish fighters in northern Syria pounding them with airstrikes and artillery, and complicating the battle against the Islamic State group by Ankara and Washington, both NATO allies.
In the fight for Aleppo, meanwhile, the Syrian military used a lull in violence to urge residents and rebels to evacuate the besieged opposition-held part of the city.
Turkey's state-run Anadolu news agency said as many as 200 members of the Kurdish-led forces were killed in Syria's Aleppo province by the Turkish bombing and shelling.
A senior commander with the main Syria Kurdish militia confirmed the Turkish attack on his forces north of Aleppo but disputed the casualty toll, saying that no more than 10 fighters were killed.
Like in Iraq, where Kurdish fighters are at the forefront of the offensive to retake the city of Mosul from the Islamic State group, Kurdish forces in Syria also have been battling IS militants and made significant territorial gains in Aleppo province. That has dismayed Turkey, which is dealing with a homegrown Kurdish insurgency and trying to prevent an expansion of Kurdish influence in Syria.
"We will not back down," senior Kurdish commander Mahmoud Barkhadan of the People's Protection Units told The Associated Press by telephone from the region.
"We are fighting Daesh. Why are they striking at us?" he asked, using the Arabic acronym for IS.
Barkhadan accused Turkey of aiding IS militants by turning the fight into a Turkish-Kurdish battle.
Turkish artillery also hit near Afrin, a Kurdish enclave in northwestern Syria, he said, adding that his forces have not retreated but that Turkey's actions allowed IS fighters to wage a counteroffensive.
More than 10 fighters were killed and 20 wounded in over 30 aerial attacks that began Wednesday night, he said.
The Britain-based Syrian Observatory for Human Rights said at least 14 Kurdish fighters were killed and four were missing.
Anadolu, quoting military officials, reported the raids were carried out late Wednesday night on 18 targets in the Maarraat Umm Hawsh region in northern Syria. Between 160 and 200 militia fighters were killed, it said. The targets struck areas that Syrian Kurdish forces recently took over as they pressed a campaign to drive IS militants from areas north of Aleppo.
The Syrian Kurdish forces have been a source of tension between Turkey and the United States. The U.S. considers the militia group — the People's Protection Units, known as the YPG — to be the most effective force against the IS group in Syria. Turkey calls it an extension of its own outlawed Kurdish militants who have carried out deadly attacks in Turkey and considers it a terrorist organization.
A U.S. defence official in Washington said the Syrian Kurdish fighters targeted by Turkish airstrikes Wednesday are not among the Kurdish groups that U.S. forces are advising and assisting, so there were no U.S. troops with those Kurds when they came under attack.
The official said Thursday, however, that since the Kurds who were targeted are affiliated with U.S.-backed Kurdish fighters, the Turkish attacks were problematic and have angered the U.S.-backed Kurds. The official spoke on condition of anonymity because he was not authorized to discuss the matter publicly.
In August, Turkey sent troops and tanks into northern Syria to help opposition forces drive IS away from Turkish-Syrian border areas and to curb the Syrian Kurdish forces' territorial expansion.
Ilham Ahmed, a senior Syrian Kurdish official, said the Turkish attack was an aggression on her people's aspiration for self-administration in a contiguous territory in the north as well as a threat to the U.S-led anti-terrorism fight there.
The Turkish moves threatens a possible campaign against IS in the group's de-facto capital of Raqqa in eastern Syria, Ahmed said. Kurdish forces are the main partner in such a fight, but Ankara has said it is ready to act without Kurdish participation.
Ahmed said Turkey is taking advantage of U.S. attention being focused on its presidential election to push back against the Kurds and advance in northern Syria.
Washington is "asked to put a stop and take a clear and direct position regarding this Turkish aggression. Otherwise, the project of combatting terrorism may be delayed or totally fail in Syria," she said, speaking from Sulaimaniyah, Iraq.
Anadolu said the 18 Syrian Kurdish targets hit included nine buildings used as headquarters, meetings points, shelters or arms depots, along with five vehicles.
The pause in the fighting in Aleppo is part of a humanitarian cease-fire announced by Russia in the contested city to allow for the evacuation of civilians and fighters, as well as the wounded. Rebels have rejected the offer to evacuate, saying it wasn't serious.
Clashes were heard at one of the safe corridors announced by the Syrian military.
"Talk of fighters or non-fighters leaving is denied and groundless," said Ammar Sakkar, spokesman for Fastaqim, one of the largest rebel groups operating in Aleppo. "The rebels' decision has not and will not change. It is to be steadfast."
Eastern Aleppo, besieged by government troops, has been subjected to intense and relentless airstrikes by Syrian and Russian aircraft in recent weeks.
U.N. Secretary-General Ban Ki-moon told an emergency meeting of the U.N. General Assembly that nearly 500 people have been killed and almost 2,000 injured since the Syrian government launched its offensive in eastern Aleppo on Sept. 23.
Ban said the city's besieged district has seen "the most sustained and intensive aerial bombardment" since the conflict began 5 1/2 years ago.
He warned that "food rations will run out by the end of the month."
The secretary-general said the bombing pause will hopefully allow urgent medical evacuations and delivery of emergency medical and humanitarian supplies, but he stressed that "this is the bare minimum."
At a checkpoint in the rebel-held east, government loudspeakers blared: "Our dear people in Aleppo districts, let the wounded and sick leave. ... We guarantee you safe passage. Seize the opportunity and protect your families' lives." They offered a warm meal and medical help along the way.
"There is no point in continuing to fight. Your positions and bases and warehouses are known to us precisely. Don't use civilians as human shields," the announcements said.
But there were no takers Thursday, with residents saying they did not trust the promise in the absence of international monitors.
U.N. Syria envoy Staffan de Mistura insisted a unilateral cease-fire aims only to allow medical evacuations and is not part of a broader plan that he has laid out for Aleppo, countering an assertion by Syrian President Bashar Assad that most civilians want to leave.
But de Mistura told the General Assembly later that "in this current lull in bombardment, we hope this is more than just a temporary initiative."
If it is temporary, "which is what we have been so far told, then we do fear that if the previous level of bombing resumes ... eastern Aleppo could end up being destroyed before Christmas and the end of this year," he said.
Senior U.N. aid official Jan Egeland told the AP that the U.N. received verbal assurances for the extension of the three-day pause by another day until Monday to allow for the U.N.-supervised medical evacuation of wounded from the city.
Russian Defence Minister Sergei Shoigu confirmed an extension but only mentioned the pause was being prolonged by one day. The discrepancy between the statements could not immediately be reconciled.
Egeland said talks are continuing with armed opposition groups on the deal. He said he expects medical supplies to be allowed in.
Ibrahim al-Haj, a resident of eastern Aleppo and a volunteer with the White Helmets team of first responders in the city, said no one trusts safe passages without U.N. supervision.
"If there is no corridor with international supervision, it is impossible anyone would leave," al-Haj said, adding that shots were fired over the heads of some who approached the crossing Thursday. He blamed government snipers.
Fraser reported from Ankara, Turkey. Associated Press writers Jamey Keaten in Geneva, Robert Burns in Washington, Vladimir Isachenkov in Moscow and Edith M. Lederer at the United Nations contributed.