Defense Secretary Ashton Carter testifies at a Senate Armed Services Committee hearing on the Obama administration's strategy to counter the Islamic State. (Jim Lo Scalzo/EPA)

Defense Secretary Ashton B. Carter on Tuesday visited a Turkish air base near the Syrian border that has become a hub for operations against the Islamic State, as the Obama administration presses Turkey and other allied nations to step up their military response to the extremist group.

Carter touched down at Incirlik, located in southern Turkey about 100 miles from the Syrian border, at the beginning of a Middle Eastern tour that will give him a chance to assess the evolving U.S. campaign against the militant group, which remains dug in across large tracts of Syria and Iraq despite 16 months of U.S. and allied airstrikes.

“We’re looking to intensify and accelerate the defeat of ISIL,” Carter told reporters from the base’s sprawling tarmac. The Islamic State, a radical al-Qaeda offshoot, is also known as ISIS and ISIL.

The visit comes a day after President Obama convened an unusual meeting of top national security officials at the Pentagon to examine plans for battling the Islamic State. In the wake of terrorist attacks in Paris and San Bernardino, Calif., Obama has sought to reassure Americans about his strategy for combating the group overseas and preventing attacks at home.

While U.S.-backed forces in Iraq and Syria have made progress in dislodging Islamic State fighters from some areas, satellite groups have gained momentum, illustrating the challenge of containing loosely linked militant organizations in regions as distant from one another as North Africa and South Asia.

The Pentagon in recent weeks has rolled out a series of new steps designed to make its campaign more effective, including establishing a new Special Operations task force in Iraq and sending a small number of elite U.S. troops into Syria. Now, Carter and other military leaders have promised to make further changes as they evaluate what has worked and what has not.

While France and Germany have recently expanded their military efforts against the Islamic State, Carter said that others — including Turkey, Arab states of the Persian Gulf and additional European nations — should do the same.

“We need Turkey, like other members of the coalition, to step up and do more,” he said. The Obama administration, he continued, wants partners “to get in the game militarily and hasten the destruction of ISIL.”

One focus for U.S. officials is Turkey’s extensive border with Syria, which the Islamic State and other armed groups have long used for smuggling contraband and fighters. The movement of Islamic State militants out of Syria takes on new urgency after the Nov. 13 attacks in Paris, where a cell of Islamic State supporters, some of whom had fought with the group in Syria, killed 130 people.

“It’s about stopping the flow in both directions,” Carter said.

While Carter said Turkey has taken steps to improve border security, U.S. officials privately said it has not employed its forces the way it could.

As Ankara and Washington confront the shared Islamic State threat, they must also manage the differences in their approaches to Syria’s civil war.

Turkey, eager to see the departure of Syrian President Bashar al-Assad and keep Kurdish ambitions in check, has pushed for more aggressive U.S. actions in Syria, including the establishment of a safe zone.

The United States, meanwhile, has sought to defuse Turkish tensions with Russia over Moscow’s air campaign and with Iraq over Turkey’s deployment of soldiers there.

It was Carter’s first visit as defense secretary to Incirlik, an increasingly important site in the U.S. campaign against the Islamic State. Since U.S. aircraft began flying strike missions this past summer, the number of U.S. personnel at the base has grown from several hundred to around 1,300.

The base now hosts a growing air fleet from countries such as Turkey, the United States, Qatar and Germany. About 45 of the 59 manned and unmanned aircraft stationed there are American; that fleet includes A-10 Thunderbolts, KC-135 tanker planes, F-15 fighter jets and drones.

The base’s location allows U.S. aircraft closer access to contested areas of northwestern Syria.

Col. Sean McCarthy, a pilot from the 447th Air Expeditionary Group, said Incirlik now accounts for a third of refueling flights for the Iraq and Syria campaign. “What Incirlik represents is that final link in the noose” around the Islamic State, he said.

During his visit, Carter also met with officials overseeing the new program to send U.S. Special Operations forces into Syria.