Hundreds of Kurdish fighters have crossed from Turkey into neighbouring Syria to defend a Kurdish area under attack by Islamic State militants, activists said.
Fighting there led another prominent Kurdish official to appeal for international assistance in their battle against the extremists.
The movement of hundreds of Kurdish fighters into Syria reflected the ferocity of the fighting in the northern Kobani area, which borders Turkey. Militants of the extremist Islamic State group have been barrelling through the area over the past three days, seizing villages and forcing tens of thousands of Syrian Kurds to flee.
"Kobani is facing the fiercest and most barbaric attack in its history," said official Mohammed Saleh Muslim, head of Syria's Kurdish Democratic Union. The groups' members dominate the Syrian Kurdish group known as the YPK, which is fighting the Islamic State militants.
"Kobani calls on all those who defend humane and democratic values... to stand by Kobani and support it immediately. The coming hours are decisive," he said.
The Britain-based Syrian Observatory for Human Rights and Kurdish official Nawaf Khalil said that the fighters were streaming into the Kobani. The Observatory estimated their numbers in the hundreds.
Syrian Kurdish fighters had been successfully fighting off the militants for the past two years. They even clashed with the Islamic State group's fighters in northern Iraq, carving a safe passage for thousands of embattled Iraqis of the Yazidi minority, whom the militant group sees as apostates.
But the tide changed in September. Islamic State group fighters, using weapons and armour seized from Iraqi soldiers who fled the militants' advance in June, are now sweeping through the Kobani area.
As the fighting continued, Mr Khalil said Kurdish fighters had evacuated several other villages pre-emptively to ensure the safety of residents. At least 45,000 Syrian Kurds had crossed into Turkey since Friday, Turkish deputy prime minister Numan Kurtulmus said.
"Some of our brothers are being placed with their relatives, some are being taken to local schools and state facilities, others are being hosted in tents," Mr Kurtulmus said.