The main Kurdish armed group in Syria called on its kinsmen across the region to help it stop a massacre in the Syrian town of Kobani as Islamic State militants armed with tanks edged closer on its outskirts and pummeled it with artillery fire.
Islamic State's battlefield gains in recent months have come as Syrian President Bashar al-Assad's forces have focused on other rebel groups. On Friday the army advanced on the city of Aleppo further west, threatening rebel supply lines in a potentially major reversal.
U.S.-led forces have been bombing Islamic State targets in Syria and Iraq but the action has done little to stop the group's advance in northern Syria towards the Turkish border, piling pressure on Ankara to intervene.
Canada said it would send fighter jets and other aircraft to take part in the U.S.-led strikes on Islamic State in Iraq for a period of up to six months.
Turkey said it would do what it could to prevent Kobani, a predominantly Kurdish town just over its southern border, from falling into Islamic State. It has stopped short of committing to any direct military intervention and Syria warned on Friday against any Turkish "aggression" on its territory.
A statement issued by the YPG, the main Kurdish armed group, vowed "never ending" resistance to Islamic State in its advance on Kobani. "Every street and house will be a grave for them."
"Our call to all the young men and women of Kurdistan ... is to come to be part of this resistance."
Esmat al-Sheikh, head of the Kurdish forces defending Kobani, said the distance between his fighters and the insurgents was now less than one kilometer (half a mile).
"We are in a small, besieged area. No reinforcements reached us and the borders are closed," he told Reuters by phone. "My expectation is for general killing, massacres and destruction."
Islamic State has carved out swathes of eastern Syria and western Iraq in a drive to create a caliphate between the Euphrates and the Tigris rivers. Kobani's resistance has prevented it from consolidating territory across Syria's north.
Fighting continued after the sun set, with artillery strikes on residential areas east and southwest of Kobani's center. Kurds returned fire, and red tracer bullets targeting Islamic State strongholds east of the city flew over rooftops, a Reuters correspondent on the Turkish side of the border said.
Remzi Savas, 53, smoked a cigarette and listened to the gunfire over the border.
"My son is over there, he crossed through a minefield to get there. He is just 14. There are many children fighting for the YPG, we can't hold them back. They think they'll lose everything if Kobani falls."
The British-based Syrian Observatory for Human Rights said at least 80 shells had hit the town, known as Ayn al-Arab in Arabic, and there were heavy clashes in the east and southeast.
The fighting has driven Kurds from across northern Syria from their homes across the border into Turkey.
"It's a dramatic humanitarian tragedy as we have all witnessed," U.N. High Commissioner for Refugees Antonio Guterres said in Geneva. "It's the largest single outflow of Syrians in a few days, 160,000 people."
Further west, a Syrian army advance threatened to take the last main rebel supply route leading into Aleppo from the north and reverse two years of gains by Assad's foes.
"They are going to encircle Aleppo," said Abu Abdo Salabman, a member of the political office of the Mujahideen Army, a rebel group viewed as part of the moderate opposition to Assad.
"They are bombing us non-stop," said Salabman, who was not using his real name. "They are marching on us and the regime air force is non-stop."
The Syrian army has taken control of three villages, state television said, in a campaign by Assad's forces that could encircle insurgents in the city.
Although there are smaller, more indirect routes into Aleppo, taking the northern road would also allow the army to besiege areas of the city which fell to insurgents in 2011, a tactic it used to retake Homs city in May.
Assad's forces are fighting a mixture of rebel groups in Syria, including Islamic State but also a mix of western-backed forces in a conflict which has killed nearly 200,000 people.
This year, Washington and its allies have shifted focus in Syria from battling Assad to combating Islamic State.
The U.S. military said coalition forces carried out strikes in Iraq and Syria overnight on Thursday. In Syria they destroyed an Islamic State garrison, two of the militant group's tanks and hit two mobile oil refineries and a training camp.
In Iraq, government forces recaptured the town of Dhuluiya, about 70 km (45 miles) north of Baghdad, which had been under siege by Islamic State.
Prime Minister Haider al-Abadi called on Iraq's bickering political factions to unite. In a message to mark the Muslim holy feast of Eid, he said the battle against Islamic State would continue to the end.
Village by village, Kurdish forces in northern Iraq have regained around half the territory they gave up in August when Islamic State militants tore through their defenses in the northwest, prompting the United States to launch air strikes in September, its first since 2011.
Turkey, however, insists the air strikes alone will not contain the Islamic State threat, and wants simultaneous action to be taken against Assad's government, including the creation of a no-fly zone on the Syrian side of the border.
Prime Minister Ahmet Davutoglu said Turkey would do what it could to prevent Kobani from falling to the militants but stopped short of committing to the sort of intervention Kurds have called for.
"We wouldn't want Kobani to fall. We'll do whatever we can to prevent this from happening," Davutoglu said in a discussion with journalists broadcast on the A Haber television station.
Parliament gave the government powers on Thursday to order cross-border military incursions against Islamic State, and to allow forces of the U.S.-led foreign coalition to launch similar operations from Turkish territory.
Syria said Turkey's decision was an act of aggression which could have "catastrophic consequences".
But Davutoglu appeared to pull back from any suggestion that Turkey was planning a military incursion, saying this could drag Ankara into a wider conflict along its 900 km (560-mile) border.
Ankara fears intervention could worsen security on its border by strengthening Assad and bolstering Kurdish fighters linked to the Kurdistan Workers Party (PKK), which has waged a three-decade insurgency against the Turkish state.