Kurdish fighters backed by US-led coalition air strikes are locked in a fierce battle to prevent a key Syrian border town from falling into the hands of jihadists.
The air strikes and heavy clashes in Ain al-Arab on the border with Turkey - a crucial recent battleground in the fight against the Islamic State group - left at least 18 people dead, including nine jihadists and nine Kurdish fighters, monitors said.
Ambulances ferried wounded fighters for treatment in Turkey as mortar exchanges continued on Wednesday, with some rounds hitting very close to the border, an AFP correspondent on the Turkish side reported.
As the battle raged, Syria's three-and-a-half year civil war claimed more lives - with twin car bombings in the government-controlled city of Homs killing at least 18 people - and Kurdish fighters in Iraq pursued their own advance against IS jihadists.
At Ain al-Arab, Kurdish forces have been on the retreat for more than two weeks in the face of a jihadist assault that sent tens of thousands of refugees streaming across the border.
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With IS fighters less than three kilometres from the town, the US-led coalition carried out at least five air strikes on Wednesday, the Syrian Observatory for Human Rights said.
The Britain-based monitoring group said the strikes hit IS fronts south and southeast of the town, known as Kobane by the Kurds, adding that at least eight jihadist fighters were killed in one of them.
One other jihadist and nine Kurdish fighters were killed in the overnight clashes, it said.
Ain al-Arab would be a key prize for IS, giving it unbroken control of a long stretch of the Syrian-Turkish border.
In Homs, children were among the 18 people killed in the twin car bombs near a school, the Observatory said.
The blasts struck in a neighbourhood of the city mainly inhabited by the Alawite community of Syrian President Bashar al-Assad which has been frequently targeted by the mainly Sunni Muslim rebels.
The US-led coalition of Western and Arab allies is providing air support to local forces in their ground war against IS, an extremist Sunni group that has seized control of large parts of Syria and Iraq.
The US launched strikes in Iraq in August and has been joined by Western allies. Last week, Washington and Arab states also began hitting IS targets in Syria.
In Iraq, Kurdish fighters were advancing against IS militants on three fronts, with support from British and US air strikes.
Backed by 11 coalition strikes, Kurdish forces went on the offensive on Tuesday in the town of Rabia on the Syrian border, north of jihadist-controlled second city Mosul, and south of oil hub Kirkuk, commanders said.
Further south, Sunni Arab tribesmen opposed to IS repelled a renewed jihadist attack on their neighbourhood in the town of Dhuluiyah in fighting that killed 14 people, police and medics said.
The Pentagon appealed for patience, warning that there would by no quick and easy end to the fighting.
"No one should be lulled into a false sense of security by accurate air strikes," the Pentagon spokesman, Rear Admiral John Kirby, told reporters.
"We will not, we cannot bomb them into obscurity."
A long-term effort will be needed to train and arm Syrian rebel forces and strengthen Iraq's army, he said.
NATO member Turkey, after months of caution in the fight against IS, has decided to harden its policy, and the government asked parliament on Tuesday to authorise military action against IS in Iraq and Syria.
MPs are due to debate a motion on Thursday that Deputy Prime Minister Bulent Arinc said would "meet all the demands and eliminate the risks and threats".
