Smoke rises after an US-led air strike in the Syrian town of Kobani Ocotber 9, 2014. Islamic State fighters have seized more than a third of the Syrian border town of Kobani despite US-led air strikes targeting them in and around the mainly Kurdish community, a monitoring group said on Thursday. [Photo/Agencies]

MURSITPINAR, Turkey/BEIRUT - Islamic State fighters seized more than a third of the Syrian border town of Kobani, a monitoring group said on Thursday, as US-led airstrikes failed to halt their advance and Turkish forces nearby looked on without intervening.

With Washington ruling out a ground operation in Syria,Turkey described as unrealistic any expectation that it would conduct a cross-border operation unilaterally to relieve themainly Kurdish town.

The commander of Kobani's heavily outgunned Kurdish defenders said Islamic State controlled slightly less than a third of the town that lies within sight of Turkish territory.

However, he acknowledged that the militants had made major gains in a three-week battle that has also led to the worst streets clashes in years between police and Kurdish protesters across the frontier in southeast Turkey.

The Syrian Observatory for Human Rights said Islamic State, which is 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 whichmonitors the Syrian civil war.

Esmat al-Sheikh, leader of the militia forces in Kobani, said Islamic State had seized about a quarter of the town in the east. "The clashes are ongoing - street battles," he told Reuters by telephone from the town.

Explosions rocked the town throughout Thursday, with blacksmoke visible from the Turkish border a few kilometres (miles) away. Islamic State hoisted its black flag in Kobani overnight and a stray projectile landed 3 km (2 miles) inside Turkey. The US-led coalition carried out several airstrikes on Thursday and sporadic gunfire from the besieged town was audible.

The United Nations says only a few hundred inhabitants remain in Kobani but the town's defenders say the battle will end in a massacre if Islamic State prevails, giving it a strategic garrison on the Turkish border.

They complain that the United States is giving only tokensupport through the air strikes, while Turkish tanks sent to thefrontier are looking on but doing nothing to defend the town.

Turkish Foreign Minister Mevlut Cavusoglu played down thelikelihood of those forces going to the aid of Kobani.

"It is not realistic to expect Turkey to conduct a groundoperation on its own," he told a joint news conference withvisiting NATO chief Jens Stoltenberg. However, he added: "We areholding talks.... Once there is a common decision, Turkey willnot hold back from playing its part."

Ankara resents any suggestion from Washington that it is notpulling its weight, but wants broader joint action that alsotargets the forces of Syrian President Bashar al-Assad. "Westrongly reject allegations of Turkish responsibility for theISIS advance," said a senior Ankara government source.

"Our allies, especially the US administration, draggedtheir feet for a very long time before deciding to take actionagainst the catastrophic events happening in Syria," he added.

Turkey has long advocated action against Assad during thecivil war, which grew out of a popular uprising in 2011.

However, the United States called off air strikes on Damascusgovernment forces at the last minute last year when Assad agreedto give up his chemical weapons.

President Tayyip Erdogan says he wants the US-led allianceto enforce a "no-fly zone" to prevent Assad's air force flyingover Syrian territory near the Turkish border and create a safearea for an estimated 1.5 million Syrian refugees in Turkey toreturn.

But Stoltenberg said that establishing a no-fly zone or asafe zone inside Syria has not been discussed by NATO.