U.S. Secretary of State John F. Kerry waits for a meeting with Turkish Prime Minister Ahmet Davutoglu, not pictured, at the prime minister’s office in Ankara. (Brendan Smialowski/Pool photo via Reuters)

Turkey will be an important part of the international military and diplomatic coalition fighting Islamic State militants, whether or not the Muslim nation on Syria’s border makes public declarations of support or allows American warplanes to use its bases, U.S. officials said Friday.

Secretary of State John F. Kerry courted Turkish leaders one day after Turkey abstained from a declaration of support for the campaign signed by Arab diplomats in Saudi Arabia. An unidentified Turkish official was widely quoted this week as saying Turkey would not allow military bases on its territory to be used for airstrikes in Syria or Iraq.

Kerry said it is “premature” to discuss Turkey’s role or the precise commitments of any nation as an international coalition forms to confront the militants.

“Within the coalition, there are many ways Turkey can help,” Kerry told reporters after a day of discussions in the Turkish capital. “We will continue our conversations with our military and other experts to define the specific role that Turkey will play.”

Turkey does not publicly acknowledge that unarmed U.S. military surveillance drones are flown over Iraq from Incirlik Air Base, where a U.S. Air Force wing is based. Turkey refused a U.S. request to use its territory as a base for operations during the Iraq war.

Kerry announced that retired Marine Gen. John R. Allen will become President Obama’s special envoy for the global coalition launched this week with Obama’s pledge to defeat the Islamic State. Allen is a longtime Middle East expert and troubleshooter whose last military assignment was command of international forces in Afghanistan. Reporting to Kerry, he will match requirements of the campaign against the militants with potential contributors, the State Department said.

The military portion of the campaign against the Islamic State would be hobbled without help from Turkey. The NATO member borders Syria and Iraq to their north, and it is a transit route for foreigners seeking to join the fight and for oil commandeered by militants to come out to market. Turkey’s strategic importance is clear from the fact that Defense Secretary Chuck Hagel visited three days before Kerry , carrying the same message.

However, nearly 50 Turkish diplomats and staffers have been held hostage since Islamic State militants overran the Turkish consulate in Mosul, Iraq, in June, complicating Turkey’s response to the crisis and potentially delaying any statement of support for U.S. and other efforts. Turkish President Recep Tayyip Erdogan has warned against jeopardizing any effort to win the release of his country’s diplomats.

Still, the militant network is a growing threat to Turkey, and leaders of the Muslim-majority nation support the international effort, U.S. officials said ahead of Kerry’s visit.

U.S. airstrikes already underway in Iraq are expected to be expanded to Syria, a haven for the militants, but thus far, no other nation has publicly pledged to send its own planes. Britain, whose participation in the Iraq war was hugely unpopular at home, gave conflicting statements this week about its willingness to take part in airstrikes in Syria. U.S. officials have said they need more help in the region with refueling of aircraft, airlifting of equipment and supplies, and providing help to moderate Syrian rebel groups.

U.S. officials have complained that Turkey does too little to police its porous border with Syria, allowing untold thousands of fighters from Europe and North Africa to cross over, along with supplies. “There’s been improvement, but additional improvement needs to be made,” one senior State Department official said Friday.

That official and others traveling with Kerry spoke on the condition of anonymity to discuss sensitive diplomacy. They highlighted newly released Turkish statistics saying that some 6,000 people were denied entry into Turkey because of suspicions that they were traveling to join the fight. Turkey says an additional 1,000 were recently deported. Turkey also detained a Frenchman suspected of being a top recruiter of foreign fighters and turned him over to French authorities this week.

“Obviously, there are some sensitivities that Turkey has, and we are cognizant of that and respect that,” one State Department official said. “But they are an important counterterrorism partner, and that’s why we have certainly had an uptick in our meetings and engagements with them.”

Turkey and the United States had given each other the diplomatic cold shoulder for more than a year over differences including U.S. concerns about Erdogan’s increasingly antidemocratic shift while he was prime minister and his hostile language about Israel. The United States has said little about Erdogan’s recent remark that Israel behaved “like Hitler” in the Gaza Strip during its seven-week war with Hamas this summer but snubbed the Turkish president by sending no Washington officials to his inauguration in August.

Turkish Foreign Minister Mevlut Cavusoglu shook hands with Kerry for news cameras and warmly welcomed him to Ankara, but he made no promises of Turkish support and took no questions. Reporters were kept away from Kerry’s other meetings, including with Erdogan.

Also Friday, the United States pledged nearly $500 million in additional humanitarian aid for refugees and other victims of the Syrian civil war, marking a significant boost in U.S. relief funding in the region. The United Nations estimates that nearly 3 million people have fled Syria during more than three years of fighting. Millions more have been displaced inside Syria.

The commitment brings total U.S. humanitarian spending to roughly $3 billion since the start of the conflict in March 2011.