A convoy of pro-government fighters entered Syria's Afrin region on Tuesday, a local official and a monitor told AFP, as Turkey pressed its assault on the Kurdish-controlled enclave.
"The popular forces have entered the Afrin canton," said Rojhad Rojava, a Kurdish defence official in the local administration.
The Syrian Observatory for Human Rights, a Britain-based war monitor, said that "hundreds of fighters" entered the Afrin region on Tuesday afternoon.
AFP correspondents said the forces did not appear to have entered Afrin city itself.
Ankara and allied Syrian rebels launched an offensive exactly one month ago against the Kurdish People's Protection Units (YPG) in the northwestern region.
The YPG has controlled Afrin since Syrian government forces withdrew from Kurdish-majority areas in the country's north in 2012.
But on Monday, Syria's state media reported that pro-Damascus forces would head to Afrin to "join the resistance against the Turkish aggression".
"This comes in the framework of supporting residents and defending the territorial unity and sovereignty of Syria," news agency SANA said.
The Afrin region lies in Syria's northern province of Aleppo.
An AFP correspondent in government-controlled Aleppo city told AFP that a convoy of pick-up trucks carrying armed men had left earlier Tuesday en route to Afrin.