Islamic State fighters seized more than a third of the Syrian border town of Kobani, a monitoring group said on Thursday, as U.S.-led air strikes failed to halt their advance and Turkish forces looked on without intervening.
With Washington ruling out a ground operation in Syria, Turkey said it was unrealistic to expect it to mount a cross-border operation alone to relieve the mainly Kurdish town.
The U.S. military said Kurdish forces appeared to be holding out in the town, which lies within sight of Turkish territory, following new air strikes in the area against a militant training camp and fighters.
Washington said U.S. forces launched nine air strikes on Thursday against Islamic State militants north and south of Kobani, striking some fighting units and destroying four buildings held by the group. U.S. forces also conducted two air strikes against Islamic State in Iraq.
But the Syrian Observatory for Human Rights said Islamic State, still widely known by its former acronym of ISIS, had pushed forward on Thursday.
"ISIS control more than a third of Kobani - all eastern areas, a small part of the northeast and an area in the southeast," said Rami Abdulrahman, head of the Observatory, which monitors the Syrian civil war.
The commander of Kobani's heavily outgunned Kurdish defenders confirmed that the militants had made major gains, after a three-week battle that has also caused the worst street clashes in years between Turkish police and Kurdish protesters.
In Turkey's eastern province of Bingol, two police officers were killed and a police chief was seriously wounded in an attack, CNN Turk television reported, while clashes elsewhere killed four protesters.
Militia chief Esmat al-Sheikh put the area controlled by Islamic State, which controls large amounts of territory in Syria and neighboring Iraq, at about a quarter of the town. "The clashes are ongoing, street battles," he said by telephone from the town.
Explosions rocked Kobani throughout the day, with black smoke visible from the Turkish border a few km (miles) away. Islamic State hoisted its black flag in the town overnight and a stray projectile landed 3 km (2 miles) inside Turkey.
The town's defenders say the United States is giving only token support with its air strikes, while Turkish tanks sent to the frontier look on but do nothing to defend the town, where the United Nations says only a few hundred remain. Over 180,000 people from the city and surrounding area have fled into Turkey.
Turkey's foreign minister, Mevlut Cavusoglu, played down the chances of its forces going to the aid of Kobani.
"It is not realistic to expect Turkey to conduct a ground operation on its own," he told a news conference with visiting NATO chief Jens Stoltenberg. He added: "We are holding talks ... Once there is a common decision, Turkey will not hold back from playing its part."
Ankara resents suggestions from Washington it is not pulling its weight, and wants broader joint action that also targets the forces of Syrian President Bashar al-Assad. "We strongly reject allegations of Turkish responsibility for the ISIS advance," said a senior Ankara government source.
"Our allies, especially the U.S. administration, dragged their feet for a very long time before deciding to take action against the catastrophic events happening in Syria," he added.
Turkey has long advocated action against Assad during the civil war, which grew out of a popular uprising in 2011. But the United States called off air strikes on Damascus government forces at the last minute last year when Assad agreed to give up his chemical weapons. It has also managed so far to fly sorties across Syria with tacit consent from Assad.
Kerry said Islamic State's advance on Kobani was a tragedy but would not deter the U.S. coalition from its long-term strategy in the region.
"Kobani is a tragedy because it represents the evil of ISIS, but it is not the definition either of the strategy or the full measure of what is happening with response to ISIS," he told reporters in Boston.
"We are only a few weeks into building the coalition," Kerry said. "The primary goal of this effort has been to provide the space for Iraq to be able to get its government in place and to begin to push back and to begin to be able to deprive them (Islamic State militants) of their command and control, their supply centers and their training. That is taking place."
Retired U.S. General John Allen, asked by President Barack Obama to oversee the creation and work of the anti-Islamic State coalition, was in Ankara on Thursday for two days of talks with Turkey's leaders.
President Tayyip Erdogan wants the U.S.-led alliance to enforce a "no-fly zone" to prevent Assad's air force flying over Syrian territory near the Turkish border, and to create a safe area for around 1.5 million Syrian refugees in Turkey to return.
Stoltenberg said neither had been discussed by NATO.
The anger felt by Turkey's Kurds over Ankara's failure to help their brethren in Syria threatens to unravel a fragile peace process that Erdogan hoped would end a 30-year armed struggle for autonomy by the Kurdistan Workers' Party (PKK).
At least 25 people died in the mainly Kurdish southeast of Turkey on Wednesday during clashes between security forces and Kurds demanding that the government do more to help Kobani.
On Thursday, two policemen came under attack in Bingol's city center while they were inspecting shops damaged in demonstrations earlier this week. No group claimed responsibility for the killings.
Four people were killed and 20 were wounded in the southern border province of Gaziantep when armed clashes broke out between protesters demonstrating in solidarity with Kobani and groups opposing them.
The violence had prompted curfews to be imposed in five southeastern provinces, restrictions unseen since the height of the PKK's war against Turkish forces in the 1990s, and streets were calmer as a result.
Erdogan said protesters had exploited the events in Kobani as an excuse to sabotage the peace process.
Selahattin Demirtas, head of the Kurdish People’s Democratic Party (HDP), which had urged Turkish Kurds to take to the streets this week, denied that they had provoked violence. He appealed for calm and said jailed PKK leader Abdullah Ocalan had called for talks with the government to be stepped up.
Kurdish leaders in Syria have asked Ankara, so far in vain, to establish a corridor through Turkey to allow aid and possibly arms and fighters to reach Kobani.
Ankara is suspicious of Syria's Kurds for having achieved self-rule by tacit agreement with Assad after he lost control of the region to anti-government rebels, and fears this could revive secessionist aspirations among its own Kurds.
Turkish police fired tear gas against Kurdish protesters in the town of Suruc near the border overnight, and the shutters of most shops remained closed in a traditional mark of protest.
Ferdi, a 21-year-old Turkish Kurd watching the smoke rising from Kobani, said if the town fell, the conflict would spread to Turkey. "In fact," he said, "it already has spread here."