WASHINGTON (AP) -- In a fresh test for U.S. coalition-building efforts, Turkey is launching airstrikes against Kurdish rebels inside its borders this week despite pleas from the Obama administration to instead focus on an international campaign to destroy Islamic State militants wreaking havoc in the region.

Media reports about the Turkish strikes surfaced Tuesday as President Barack Obama and military chiefs from more than 20 nations gathered in Washington in a show of unity against the Islamic State group.

"This is an operation that involves the world against ISIL," Obama declared, referring to the militant group by one of its many names.

The Turkish airstrikes occurred Monday and marked the country's first major strikes against Kurdish rebels on its own soil since peace talks began two years ago. The strikes came amid anger among the Kurds in Turkey, who accuse the government there of standing by while Syrian Kurds are being killed by Islamic State militants in the besieged Syrian border town of Kobani.

The Islamic State militants also have targeted Kurds in Iraq, who have to some extent been able to hold off their advances.

The U.S. has been pressing Turkey - a NATO ally - to take a more active role in the campaign to destroy the Islamic State group, but the Turks have said they won't join the fight unless the U.S.-led coalition also targets Syrian President Bashar Assad's government. The Obama administration sees those as separate fights and has no appetite to go to war against Assad.

Officials from Ankara participated in Tuesday's meeting at Andrews Air Force Base, Maryland. A U.S. military official familiar with the talks said the chiefs of defense agreed to recommend to their governments that they continue to move forward together against the extremists, "to contribute capabilities best suited to each nation, and to take action to build on the successes already achieved by coalition efforts on the ground and in the air." The official requested anonymity for providing the information.

Earlier Tuesday, the U.S.-led coalition stepped up attacks on Islamic State targets in Kobani, launching 21 airstrikes in and around the town. One of the strikes targeted the Tel Shair hill that overlooks parts of the city, according to Idriss Nassan, deputy head of Kobani's foreign relations committee.

Nassan said Kurdish fighters later captured the hill and brought down the black flag of the Islamic State group. However, the extremist group still controls more than a third of the predominantly Kurdish town.

While the White House has tried to point out progress in the campaign against the militants, the government is also preparing the American public for a military effort that could extend well beyond Obama's presidency. Officials acknowledged Tuesday that the airstrikes in Kobani may not be enough to prevent a militant takeover, given the lack of an effective fighting force on the ground.

"We certainly do not want the town to fall," White House spokesman Josh Earnest said. "At the same time, our capacity to prevent that town from falling is limited by the fact that air strikes can only do so much."

Syrian Kurds have been begging the international community for heavy weapons to help bolster their defense of Kobani. They've also called for Turkey to open the border to allow members of the Kurdish militia in northwestern Syria - known as the People's Protection Units, or YPG - to travel through Turkish territory to reinforce the city.

So far, both requests have gone unfulfilled.

The Kurds of Syria and Iraq have become a major focal point in the war against the Islamic State group, with Kurdish populations in both countries threatened by the militants' lightning advance.

Syrian and Iraqi Kurds took part in cross-border operations to help rescue tens of thousands of displaced people from the minority Yazidi group from Iraq's Sinjar Mountain in August.

Turkey, however, is wary of the Syrian Kurds and their YPG militia, which it believes is affiliated with the Kurdish PKK movement in southeast Turkey that has waged a long and bloody insurgency against Ankara. The U.S. considers the PKK a terrorist group.

The PKK and Turkey agreed to a cease-fire last year, but the agreement has begun to unravel. Asked about the reports of a resumption in strikes against the Kurdish rebels, Prime Minister Ahmet Davutoglu said Tuesday that Turkish forces took the "necessary measure" following intense "harassing fire" by the rebels on a military outpost.

"It is impossible for us to tolerate or to placate these (attacks)," Davutoglu said.

Kurds, who make up an estimated 20 percent of Turkey's 75 million people, have faced decades of discrimination, including restrictions on the use of their language. The PKK has fought Turkey for autonomy for Kurds in a conflict that has claimed tens of thousands of lives since 1984.

The U.S. has been pressing Turkey to focus its efforts on the fight against the Islamic State group, an enemy the Turkish government shares with the Kurds.

U.S. officials have pointed to some signs of cooperation from Turkey, including commitments to help stem the flow of foreign fighters across the border into Syria. The White House said Tuesday that discussions are also continuing over whether Turkey will allow the U.S. and other countries to use bases in the country to launch attacks against the Islamic State group.

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Fraser reported from Ankara, Turkey. Associated Press writers Desmond Butler, Lefteris Pitarakis and Ryan Lucas in Turkey, Bassem Mroue in Beirut and Darlene Superville in Washington contributed to this report.

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