Kurdish fighters on October 11 halted a push by Islamic State jihadists toward the center of the Syrian border town of Kobani, as the UN warned that thousands of civilians risk being killed if it falls.
The attack came after IS militants captured the defenders' headquarters on October 10.
The Britain-based Syrian Observatory for Human Rights said the IS attack sparked 90 minutes of heavy fighting before the jihadists retreated.
The group, which has a wide network of sources inside Syria, said U.S.-led coalition warplanes launched two air strikes against IS targets south and east of town early on October 11.
The observatory said at least 554 people have been killed in and around Kobani since the IS advance began -- 298 IS militants, 236 Kurdish fighters, and 20 civilians.
The UN envoy for Syria, Staffan de Mistura, has warned that 12,000 or so civilians still in or near Kobani, including about 700 mainly elderly people in the town center, "will most likely be massacred" if the town falls.
De Mistura said on October 10 that Kobani was "literally surrounded" except for one narrow corridor to the Turkish border.
He said he feared a repeat of the 1995 Srebrenica massacre in Bosnia when thousands died and urged Turkey to allow volunteers and equipment in to help defend the town.
UN Secretary-General Ban Ki-moon also urged action to prevent a civilian "massacre" in Kobani.
Ban called in Cairo on October 12 for "all the parties to stand up to prevent a massacre of civilians in Kobani."
Kurdish diaspora around the world have protested Turkey's failure to help protect Kobani.
Turkish Foreign Minister Mevlut Cavusoglu said on October 11 that it is "unrealistic" for Turkey to allow a corridor of weapons and volunteer fighters to flow to Kobani.
In Washington, U.S. Secretary of State John Kerry warned in an interview with Voice of America on October 11 that the U.S.-led coalition will not leave the IS group "unchecked" in Syria and Iraq, despite temporary setbacks such as Kobani.
"It's just ramping up," Kerry said about the coalition's effort to combat the IS group.
Kobani's Kurdish defenders have close ties with Turkey's outlawed Kurdistan Workers Party (PKK), which has waged a three-decade insurgency for self-rule in southeastern Turkey.
Ankara has been deeply reluctant to allow weapons or Kurdish fighters to cross the border to help Kobani's defenders, despite repeated protests among its own large Kurdish minority that have left 31 people dead.
Reacting to the 31 deaths in Turkey, top PKK official Cemil Bayik said the group had called its fighters back to Turkey from bases in Iraq and could resume attacks, threatening a fragile peace process.
In Europe, more than 20,000 Kurds demonstrated against IS in the German city of Dusseldorf. About 1 million Kurds live in Germany.
In Austria, two people were seriously injured after radical Muslims attacked a Kurdish demonstration in the western city of Bregenz.
Some 5,000 to 6,000 turned out in Paris in solidarity with Kobani, as did smaller numbers elsewhere in France.
Meanwhile, U.S. officials have warned that IS fighters have been piling on pressure in neighboring Iraq, putting the army in a "fragile" position in Anbar Province between Baghdad and the border.
Some of Anbar Province fell to IS at the start of the year and most of the rest was seized by the Sunni extremists in a lightning sweep through Iraq's Sunni Arab heartland in June.
Anbar's few remaining government-controlled areas have come under repeated attack recently.
The U.S. Central Command, meanwhile, said that its planes dropped ammunition, food, and water on October 10-11 to Iraqi troops under pressure from IS in northern Iraq.
And car bombs in two Shi'ite neighborhoods of Baghdad on October 11 killed at least 34 people and wounded 54.