Attacking Islamic State jihadists met firm Kurdish resistance in the Syrian battleground town of Kobane, as neighbouring Turkey heeded pressure to intervene and handed the US access to its air bases.
In Iraq however, Islamic State (IS) fighters have government forces under strong pressure, and a roadside bomb killed the police chief in Anbar province between Baghdad and the Syrian border.
Farther north, around Iraq's key oil refinery town of Baiji, the army and Sunni Arab tribal allies came under fresh IS attack, prompting a first resupply operation by coalition aircraft.
In Kobane, on Syria's border with Turkey, a pall of black smoke hung over the strategic town as the Syrian Observatory for Human Rights reported heavy jihadist losses.
IS poured in reinforcements and fired at least 11 rocket-propelled grenades into the town centre, said the Britain-based monitoring group.
The Kurds managed to advance 50 metres (yards) towards their headquarters, two days after the jihadists captured it, but failed to deliver a knockout blow.
"They (IS) are sending fighters without much combat experience," Observatory director Rami Abdel Rahman said.
Since proclaiming a "caliphate" straddling parts of Iraq and Syria in June, the militants have seized swathes of territory and earned worldwide infamy for atrocities -- often videotaped and posted on the Internet.
Hundreds gathered Sunday in Manchester, in northwest England, for a memorial service for Alan Henning, the British hostage who was kidnapped and beheaded after travelling to Syria to help deliver aid in a convoy.
Henning's murder -- the fourth of a Western hostage since August -- has outraged the Muslim community in Britain, moderates and hardliners alike, and he was hailed as a hero at the ceremony.
- Fears for Kobane -
Turkey, which has so far been reluctant to get involved in the fighting, has faced international pressure to step in to defend Kobane.
A senior US defence official said it has now granted the United States access to its air bases for the campaign, including a key installation near the Syrian border.
"Details of usage are still being worked out," the official told AFP.
In southern Turkey, US crews have long operated out of Incirlik Air Base and about 1,500 air force personnel are stationed there. US aircraft bombing IS militants are reportedly flying out of air bases in the United Arab Emirates, Kuwait and Qatar.
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In a telephone call with Turkish Defence Minister Ismet Yilmaz, Pentagon chief Chuck Hagel thanked Turkey for its "willingness to contribute to coalition efforts, to include hosting and conducting training for Syrian opposition members," his spokesman said.
The UN has warned that hundreds of mainly elderly civilians in the centre of Kobane and thousands more on the outskirts are all at grave risk if the jihadists sever the sole escape route to the border.
UN chief Ban Ki-moon has urged action to prevent a "massacre" there.
The US military said it and its Saudi and Emirati allies conducted four air strikes in Syria Sunday, all but one in Kobane. Despite that, Pentagon officials have said there is a limit to what they can do without ground forces.
But the top US officer said American military advisers were likely to take a more direct role once Iraqi forces are ready to fight to retake the country's second city Mosul, which IS overran in June.
"My instinct at this point is that will require a different kind of advising and assisting because of the complexity of that fight," General Martin Dempsey, the chairman of the Joint Chiefs of Staff, said on ABC's "This Week".
- 'Iraqis have to take back Iraq' -
Despite deep concern about the plight of Kobane, Washington has vowed to stick to its overall strategy of prioritising the Iraq campaign.
Speaking in Cairo at a Gaza donors' reconstruction conference, US Secretary of State John Kerry said the Iraqis themselves will have to succeed on the ground to win back their country.
"Ultimately it is Iraqis who will have to take back Iraq. It is Iraqis in Anbar who will have to fight for Anbar."
Washington's strategy has seen it and its partners launch hundreds of air strikes in Iraq in support of Kurdish forces in the north and embattled federal government troops farther south.
Pro-government forces have come under particularly heavy pressure around the key oil refinery at Baiji, south of Mosul.
US defence officials have expressed mounting concern about the tenuous position of government troops, particularly in the Sunni Arab heartland north and west of Baghdad.
With federal troops on the back foot, Washington and its allies have relied heavily on Iraqi Kurdish forces in the fightback, but they too have come under pressure.
Three suicide car bombings in a Kurdish-controlled town north of Baghdad killed at least 40 people Sunday, mostly Kurdish forces veterans volunteering to re-enlist.
IS said on Twitter the bombers were German, Saudi and Turkish.