Jihadists pushed to seize Syria's Kobane and an Iraqi town close to Baghdad on Wednesday as Washington warned of a long fight against the advancing Islamic State group.
In the town of Kobane on the Turkish border, the jihadists have been holding out in fighting with Kurdish militia despite stepped-up US-led air strikes, and calls have been growing for Turkey to take action.
In Iraq, IS militants were closing on the town of Amriyat al-Fallujah, one of the last still controlled by the government in the troubled Anbar province and only 35 kilometres (20 miles) from Baghdad.
With US military officials warning that IS had the "tactical momentum", President Barack Obama told Western and Arab allies fighting IS that they are facing a "long-term campaign".
"There are not quick fixes involved. We're still at the early stages," Obama said in Washington after meeting senior commanders from more than 20 allies involved in the campaign.
"As with any military effort, there will be days of progress and there are going to be periods of setback," he added.
Obama expressed special concern for Kobane, which has become a crucial symbolic battleground in the fight against IS, and about halting the IS advance in Iraq's western Anbar province.
Fighting continued to rage for Kobane on Wednesday.
An AFP reporter across the border in Turkey reported at least four fresh US-led air strikes, after the coalition said it had hit the jihadists in Kobane with 21 raids on Monday and Tuesday alone.
A monitoring group said fighting was concentrated on the former Kurdish military headquarters in northern Kobane which IS seized on Friday.
The Britain-based Syrian Observatory for Human Rights said four coalition strikes had hit IS positions during the night, including at the headquarters.
It said Kurdish forces had retaken two IS positions near the headquarters and pushed the jihadists from several streets to its west.
Turkey, a NATO member, has stationed troops, tanks and artillery along the border -- in some cases only a few hundred yards from the fighting -- but has not intervened.
It also has yet to allow US jets to mount attacks from its territory and complicated issues Tuesday by bombing Kurdish rebel targets in the southeast of the country.
In Iraq, security forces have warned that their last position in Anbar province at the town of Amriyat al-Fallujah was under heavy pressure from the jihadists.
"IS has come from three directions; we are almost besieged," the town's police chief Aref al-Janabi told AFP by telephone.
"So far we are still standing," he said. "We have some support from tribal fighters, but if Amriyat falls, the battle will move to the gates of Baghdad and Karbala."
If the town were to be seized, IS fighters would still have to capture a significant stretch of government-controlled land before reaching the capital.
But the loss of Anbar, where government forces have suffered a string of bruising military setbacks in recent weeks, would be a heavy blow to Iraqi ground forces battling IS.
Washington has ruled out sending troops back to Iraq to take on IS, but a poll published Wednesday showed a rising number of Americans think US ground forces are needed.
Forty-one percent of those surveyed believe the fight should include both air strikes and ground troops, up from 34 percent in September, according to the NBC News-Wall Street Journal poll.
IS has seized control of large parts of Syria and Iraq, declaring a "caliphate" in June and imposing its harsh interpretation of Islamic sharia law.
The group has committed widespread atrocities, including attacks on civilians, mass executions, torture and forcing women into slavery.
US Secretary of State John Kerry on Tuesday accused IS of "abhorrent" abuses, after the jihadists boasted of selling abducted women and children from Iraq's Yazidi minority as slaves.
"ISIL now proudly takes credit for the abduction, enslavement, rape, forced marriage and sale of several thousand... women and girls, some as young as 12 years old," Kerry said in a statement, using an alternative name for the group.
"ISIL rationalises its abhorrent treatment of these women and girls by claiming it is somehow sanctioned by religion. Wrong. Dead wrong."
Thousands of foreign fighters have flocked to join IS and there are growing concerns about the group's potential appeal, especially to disillusioned young Muslims.
Malaysia was reported on Wednesday to have arrested 13 people believed to have links with IS, bringing to 36 the number of people detained in the country since April on suspicions of working with the jihadists.