By SUZAN FRASER and RYAN LUCAS, Associated Press

ANKARA, Turkey (AP) — NATO allies Turkey and the United States differed Monday on where they stand on the use of a key air base, with Turkish officials denying reports from the United States that there was a new agreement on its use for operations against Islamic State militants.

The impasse suggests that major differences remain between the two sides. Turkey has said it won't join the fight against the extremists unless the U.S.-led coalition also goes after the Syrian government of President Bashar Assad, including establishing a no-fly zone and a buffer zone along the Turkish border.

The United States has been pressing Turkey to play a larger role against the Islamic militants, who have taken control of large swaths of Syria and Iraq, including territory on Turkey's border, and sent several hundred thousand refugees fleeing into Turkey.

U.S. officials said again Monday that Turkey would let U.S. and coalition forces use its bases, including Incirlik air base, which is within 100 miles (160 kilometers) of the Syrian border, for operations against the Islamic State militants in Syria and Iraq. The officials said the details are still being worked out.

However, emerging Monday from a Cabinet meeting, Turkey's deputy prime minister, Bulent Arinc, said that "apart from the existing cooperation in combatting terrorism, there is no new situation concerning Incirlik air base."

The deputy premier added that Turkey had proposed the use of some of its bases to train and equip moderate opposition forces fighting the Islamic State group in Iraq and Syria, but said the sides had not yet come to any agreement.

Foreign Ministry spokesman Tanju Bilgic said Foreign Minister Mevlut Cavusoglu made it very clear on Monday in an interview with a Turkish news agency that "there is not an agreement — no decision has been taken as regards using Incirlik air base."

"He said that there is a consensus especially on train and equip program. But still many issues are pending and many issues are being discussed between the United States and Turkey. This includes creation of a safe zone, and creation of a no fly zone as well," Bilgic told reporters at U.N. headquarters in New York.

He said there are high-level contacts both in Turkey and the United States and the issue of bases is still on the agenda.

U.S. Defense Secretary Chuck Hagel told reporters, "I am optimistic about progress that we are making with the Turks as they, the Turks, further define their role in the coalition against ISIL," using an alternate name for the Islamic State group.

Hagel said teams from U.S. Central Command and U.S. European Command are meeting with Turkish officials and "we are making very good progress."

Hagel spoke at the end of Monday's meeting with defense ministers from the Americas at a conference in Arequipa, Peru.

Turkish Prime Minister Ahmet Davutoglu, in comments published Sunday, said Incirlik was already being used for reconnaissance purposes in Iraq and said its use for wider operations would depend on whether Turkey's demands for a no-fly zone and a safe zone in Syria are met.

"There are activities that we are already undertaking jointly from Incirlik, concerning Iraq," Davutoglu told the Milliyet newspaper. "But as a base for a more extensive operation ... we have already made our position clear: There has to be a no-fly zone and a safe haven must be declared."

Arinc said the two countries would hold "deeper" talks in the coming days on Turkey's cooperation in the U.S.-led coalition, including its demands for a no-fly zone and a safe haven in Syria.

On the ground Monday, the battle continued to rage on Turkey's border as Islamic State fighters carried out at least three suicide bombings in the Syrian border town of Kobani, allowing the group to make a small push into the strategic town, activists said.

Islamic State extremists have carved out a vast stretch of territory from northern Syria to the outskirts of Baghdad where they have imposed their harsh interpretation of Islamic law. The fighters have massacred hundreds of captured Iraqi and Syrian soldiers, terrorized religious minorities, and beheaded two American journalists and two British aid workers. Hundreds of thousands of refugees have fled into Turkey from Syria ahead of the militants.

The U.S.-led coalition has been carrying out airstrikes against militant targets in and around Kobani for more than two weeks, and the town's fate has emerged as a major test of whether the air campaign can roll back the extremists in Syria.

The sound of explosions and occasional gunfire could be heard across the border in Kobani a day after Kurdish fighters managed to slow the advance of the jihadist group. What appeared to be a rocket-propelled grenade struck a minaret in the center of the town, emitting a cloud of white smoke.

Activists said Islamic State militants were carrying out a three-pronged attack from the eastern side of the town and that clashes were reported in the southern part.

The Syrian Kurdish enclave has been the scene of heavy fighting since late last month, with the better-armed Islamic State fighters determined to capture the border post.

The Britain-based Syrian Observatory for Human Rights said an Islamic State suicide bomber detonated a car filled with explosives in the northern part of Kobani near the border with Turkey. It said the car was headed to the border crossing between Kobani and Turkey.

Later Monday, another suicide attacker blew himself up in a vehicle east of Kobani near the security quarter that houses the main police station and other local government offices, according to the Observatory and Kobani-based activist Farhad Shami.

The Observatory later reported a third suicide attack northeast of Kobani, adding that Islamic State fighters were able to capture a cultural center. Coalition warplanes later bombarded the area, the Observatory said.

Shami said the third suicide attack was carried out by an armored vehicle that blew up about 300 yards (meters) from the main border crossing point into Turkey. He also confirmed that Islamic State fighters captured the cultural center southeast of the town.

There was no immediate word on casualties from the explosions.

Shami said coalition aircraft flying over Kobani had struck 10 times Sunday and Monday.

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Lucas reported from Suruc, Turkey. AP journalists Lefteris Pitarakis in Mursitpinar, Turkey, Desmond Butler in Istanbul, Zeina Karam and Bassem Mroue in Beirut, Lebanon, and Edith M. Lederer at the United Nations contributed to this report.