Turkish guards at the border with Syria are indiscriminately shooting at and summarily returning asylum seekers attempting to cross into Turkey, Human Rights Watch said.
A senior Turkish government official denied the report Saturday, repeating that Turkey had taken in 3.5 million war refugees since the Syrian conflict began in 2011.
New York-based Human Rights Watch said Syrians were now fleeing heightened violence in the northwestern province of Idlib to seek refuge near Turkey's border, which remains closed to all but critical medical cases.
Syrian armed forces have thrust deeper into the mainly rebel-held province in recent months, and Turkey last month launched military action in the nearby Afrin region, targeting Kurdish YPG militia fighters.
"Syrians fleeing to the Turkish border seeking safety and asylum are being forced back with bullets and abuse," Lama Fakih, deputy Middle East director at Human Rights Watch, said.
President Recep Tayyip Erdogan's spokesman, Ibrahim Kalin, when asked about the HRW statement, told reporters that Turkish soldiers were there to protect these people and that Ankara has had an "open-door policy" since the start of Syria's civil war in 2011.
A senior government official later told Reuters: "There has been absolutely no case of civilians being fired upon at the border."
HRW cited U.N. figures saying 247,000 Syrians were displaced to the border area between December 15 and January 15.
"As fighting in Idlib and Afrin displaces thousands more, the number of Syrians trapped along the border willing to risk their lives to reach Turkey is only likely to increase," Fakih said.
In the latest fighting in Afrin, five Turkish soldiers were killed Saturday when their tank was hit in an attack carried out by YPG fighters, Turkey's armed forces said.
Of 16 Syrian refugees HRW spoke to, 13 alleged that Turkish border guards had shot toward them or other fleeing asylum seekers as they tried to cross while still in Syria, killing 10 people, including one child, and injuring several more.
Turkey has taken in more Syrian refugees than any other country, granting many temporary protection status and providing them with basic services, including medical care and education.
"However, Turkey's generous hosting of large numbers of Syrians does not absolve it of its responsibility to help those seeking protection at its borders," the HRW statement added.
It said Erdogan's government should issue standard instructions to border guards at all crossing points that lethal force must not be used against asylum seekers and that no asylum seeker is to be mistreated.