MURSITPINAR, Turkey — The U.S.-led coalition arrayed against Islamic State fighters conducted its most extensive air assault to date Tuesday against the extremists besieging a northern Syrian city, which Turkey’s president described as being on the verge of collapse.

“Kobani is about to fall,” President Recep Tayyip Erdogan said as he sought to counter worldwide criticism of Turkey, the easternmost bastion of the NATO alliance, for failing to act to save it.

Kobani, a largely ethnic Kurdish city just south of the Turkish border, has emerged as a global symbol of resistance to the militant group Islamic State, whose forces have overrun large tracts of Syria and northern Iraq. The Islamist fighters have mounted a three-pronged attack from the west, east and south against Kobani, also known as Ayn al-Arab.

Seizing Kobani would be a major achievement for Islamic State, opening another supply and smuggling corridor to the Turkish border from the group’s de facto capital, Raqqah, 75 miles to the southeast. Taking the Kurdish stronghold despite the U.S.-led bombing campaign would also be a huge propaganda coup.

For the Kurds, the loss of Kobani would be catastrophic, a death knell for one of the three semiautonomous Kurdish zones that have emerged in northern Syria since government forces left the area more than two years ago. Kurds have long been frustrated in their quest for independence for their homeland, which stretches over portions of Turkey, Syria and Iraq.

Outgunned but resolute Kurdish militiamen have so far held off the militants. Much of greater Kobani’s population of about 400,000 has fled the area, most to nearby Turkey.

“Kobani will not fall,” vowed Ismat Sheik, a Kurdish political representative reached Tuesday by cell phone in the besieged city. “We will resist…. We will not leave Kobani and will not give up.”

The U.S.-led coalition carried out five airstrikes overnight in the area, destroying several Islamic State vehicles and a tank and killing combatants, the Pentagon said.

Towers of smoke and debris could be seen rising above the outskirts of Kobani in the apparent aftermath of the coalition bombardment.

The air attacks were the most effective to date, according to Kurdish officials, who have previously said they were too limited and off-target. The Kurds are digging in for street battles in urban terrain that is familiar to them.

“Today they struck very well and we thank them,” said Sheik, who said at least five militant pickup trucks with mounted machine guns were destroyed. “Of course, it’s still not enough.”

Islamic State militants have reportedly penetrated Kobani’s western and southern suburbs. Several of the group’s black flags have been fluttering on the edges of town.

Erdogan, the Turkish president, gave no indication that his country was ready to do anything to halt what some fear could be an impending massacre of ethnic Kurds by the Arab forces of Islamic State. The secular Kurdish militias in northern Syria have been archenemies of various extremist Muslim factions in Syria.

The global spotlight on Kobani has been a public relations debacle for Turkey, which boasts one of the region’s largest armies and a modern air force with F-16 fighter jets. Its warplanes are not participating in the aerial assault against Islamic State in Syria, nor has Turkey given permission for U.S. fighter jets to take off from Turkish airfields.

The nation’s tanks and troops are poised directly across the border from Kobani in a fearsome array. But the Turks’ priority appears to be keeping order among protesting Kurds.

“ISIS are murderers and fanatics but Erdogan will not let anyone help us,” complained a Kurdish teenager who gave his name as Hamad and said he had been sleeping on the street along the border since being displaced two weeks ago by the militant onslaught. Islamic State is commonly referred to as ISIS, an acronym based on a former name of the group.

Turkish riot police have used tear gas and water cannons to disperse Kurds incensed that Turkey isn’t doing more and that authorities are stopping supplies and reinforcements from getting into Kobani, which has been cut off by the militants from most supply corridors in Syria.

On Tuesday, protests against the Turkish government’s stance took place in several cities in Turkey and Europe.

Turkish officials, already reeling from criticism that their policies to destabilize Syria have abetted the rise of Islamic State and other terrorist factions, are on the defensive. Analysts note that Turkey has complex and varied aims in Syria that do not coincide directly with Washington’s stated principal goal of destroying Islamic State.

The country’s major objectives include toppling the government of Syrian President Bashar Assad and crushing the Kurdistan Workers Party, or PKK, which has waged a three-decade war against the Turkish state. The Syrian Kurds holding out in Kobani are closely allied with the PKK. The Kobani episode appears to have further damaged the long-fraught relationship between Ankara, the Turkish capital, and the nation’s Kurdish minority.

For Turkish policymakers, sending armed forces on a mission that would amount to a de facto alliance with the PKK is politically unpalatable. Erdogan asserts that it is the West, not Turkey, that needs to do more.

“I am telling the West: Dropping bombs from the air will not provide a solution,” he said Tuesday during a visit to a refugee camp housing displaced Syrians.

There is widespread consensus that air power alone won’t stop the extremist forces, who are well-equipped with armored vehicles, tanks, artillery and other weapons plundered from the Syrian and Iraqi militaries.

Turkey would rather see an international force created to carve out a security corridor and no-fly zone in Syria, a massive undertaking that Washington and its allies have not embraced. Kurds view Turkey’s idea as an effort to undercut their recently won autonomy in northern Syria.

At the border, Kurdish civilians, many from Kobani, have watched helplessly as militants close in on the city. Heavy gunfire and thunderous explosions, some sending dirt and shrapnel mushrooming skyward, can be heard, as groups of furious Kurds hurl rocks at police and soldiers on the Turkish side of the border.

At the United Nations, the world body’s special envoy for Syria, Staffan de Mistura, called on the international community to defend Kobani.

“The world, all of us, will regret deeply if ISIS is able to take over a city which has defended itself with courage but is close to not being able to do so,” De Mistura said in a statement. “We need to act now.”