MURSITPINAR, Turkey (AFP) - Islamic State in Iraq and Syria (ISIS) miltants met dogged Kurdish resistance on Sunday in the high-profile Syrian battleground town of Kobane but in Iraq they put forces under strong pressure, prompting US-led relief drops.
A roadside bomb killed the police chief in Iraq's Anbar province, between Baghdad and the Syrian border, where Pentagon officials have voiced concern about the government's vulnerability to a renewed ISIS offensive.
Farther north, around the key oil refinery town of Baiji, the Iraqi army and its Sunni Arab tribal allies came under fresh attack by ISIS, prompting a first resupply operation by coalition aircraft.
In Kobane, a huge pall of black smoke hung over the strategic town as the Syrian Observatory for Human Rights reported that the extremists were taking heavy losses.
ISIS poured in reinforcements from Syria and later fired at least 11 rocket-propelled grenades into the town centre, said the Britain-based monitoring group.
The Kurds managed to advance 50 metres towards their headquarters, two days after the extremists captured it but failed to deliver a knockout blow.
"They are sending fighters without much combat experience," Observatory director Rami Abdel Rahman said. "They are attacking on multiple fronts but they keep being repulsed, then countering and being pushed back again."
ISIS has earned worldwide infamy for committing atrocities - often videotaped and posted on the Internet - since it seized swathes of Iraq and Syria in lightning offensives earlier this year.
But it has also gained prestige among Islamist extremists that has helped it recruit thousands of foreign fighters, a reputation now on the line in Kobane.
"It's a decisive battle for them," said Abdel Rahman. "If they don't pull it off, it will damage their image among jihadists around the world."
In Cairo, UN chief Ban Ki-moon urged action to prevent a "massacre" in Kobane.
The UN has warned that hundreds of mainly elderly civilians in the centre and thousands more on the outskirts all risk massacre if the militants sever the sole escape route to the border.
The US military said Sunday that it and its Saudi and Emirati allies conducted four air strikes in Syria. All but one were in Kobane, where an ISIS fighting position was among targets destroyed.
Despite such raids, Pentagon officials have said there is a limit to what they can do without forces on the ground they can work with.
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 ISIS 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 said on Sunday.
Washington has said it is deeply concerned about the humanitarian risks of Kobane's fall but vowed to keep to its overall strategy of prioritising the campaign in Iraq.
"We know there's the threat of serious casualties - that's why we're taking strikes in the Kobane area against (IS) targets," State Department deputy spokeswoman Marie Harf said. "What (ISIS) is doing in Kobane shows just how brutal these terrorists are. But the fight against (ISIS) is a much larger strategic effort than in any one town."
That strategy has seen Washington and its partners carry out hundreds of air strikes in Iraq in support of its allies - Kurdish forces in the north and embattled federal government troops farther south.
Coalition aircraft launched five strikes against ISIS in Iraq on Saturday and Sunday, the US military said.
Pro-government forces have come under particularly heavy pressure around the key oil refinery at Baiji, south of Mosul.
With the surrounding territory in ISIS hands, the coalition airdropped ammunition, food and water to its besieged defenders on Friday and Saturday in the first such resupply operation to Iraqi forces, the Pentagon said.
US defence officials have expressed mounting concern about the tenuous position of Iraqi government troops in the face of the Sunni extremists, particularly in the Sunni Arab heartland north and west of Baghdad.
Underlining that fragility, a roadside bomb on Sunday killed Anbar province police chief Major General Ahmed Saddag. He had been en route to a battleground town near the provincial capital Ramadi, one of few remaining areas of Anbar still in government hands.
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 bomb attacks targeting offices in a Kurdish-controlled town north of Baghdad killed at least 25 people Sunday, mostly Kurdish forces veterans volunteering to re-enlist.
ISIS claimed the attack via affiliated Twitter accounts, saying the bombers were from Germany, Saudi Arabia and Turkey.