A U.S. Air Force plane takes off from the Incirlik airbase, in southern Turkey on Sept. 1, 2013. Turkey has agreed to let the U.S. military use the key air base near the border with Syria to launch airstrikes against the Islamic State, senior Obama administration officials said July 23, 2015, giving a boost to the U.S.-led coalition amid a surge of violence in Turkey blamed on IS-linked militants.(AP Photo/Vadim Ghirda, File)

In a significant shift, the Turkish government appears to have approved American access to its Incirlik air base, an installation located in the country's southeast, not far from the Islamic State redoubts across the border in war-ravaged Syria.

Though details are still being thrashed out, the move is important for a number of reasons.

First, it gives the United States a far better launching point for operations targeting the Islamic State's positions in Syria, particularly in the deadly jihadist organization's de facto capital in the Syrian city of Raqqa. The shorter distance means the United States will be able to conduct longer, more effective missions pursue its targets.

Second, and more importantly, it signals Turkey's beefed-up involvement in the Syrian conflict. For many months, the United States and other Western governments have been pushing Ankara to more directly combat the extremist militants on its doorstep. Turkey's porous border with Syria has allowed the Islamic State to smuggle oil out of Syria, and bring a steady stream of foreign fighters into its ranks.

Turkey's ambivalence, particularly that of President Recep Tayyip Erdogan and the ruling Justice and Development Party, or AKP, hinged on its differing view of the conflict and the object of the U.S.-led air campaign against the Islamic State.

Erdogan was the first prominent world leader to demand the departure of embattled Syrian President Bashar al-Assad. His government was also wary of the gains being made by Syrian Kurdish factions; these militias have deep ties to Kurdish factions in Turkey, including the outlawed PKK, deemed a terrorist organization in both Ankara and Washington. As a result, some critics of Erdogan's government, particularly among Turkey's Kurdish population, argue that it tacitly abets the Islamic State. (Erdogan and his AKP allies have always rejected these claims.)

But a suspected Islamic State suicide bombing in a southern Turkish border town on Monday appeared to have tipped the balance. On early Friday, Turkish jets hit three Islamic State targets within Syria, supposedly killing 35 militants, with reports of fresh strikes the following day.

The base at Incirlik, not far from the Turkish city of Adana, has long been at the heart of U.S.-Turkish relations. It was first set up by the U.S. Air Force in 1951, a NATO installation in the shadow of the Soviet Union. Over the following decades, the base was used as a staging ground for a host of sorties and surveillance missions, including during the first Persian Gulf war.

In the late 1990s, U.S.-led patrols over a no-fly zone in northern Iraq were run from Incirlik. Micah Zenko, a fellow at the Council on Foreign Relations, explains the sorts of checks placed on these U.S. missions by Turkish authorities at the time.

When the United States led the enforcement of the northern no-fly zone over Iraq from the Incirlik Air Base in southern Turkey from 1991 to 2003, a Turkish military official at the rank of lieutenant colonel or higher was always on board U.S. Air Force AWACS planes, monitoring the airspace to assure that the United States did not violate its highly restrictive basing agreement.

Things changed dramatically in 2003, though, when the Turkish parliament voted against allowing Turkey to be a base of operations for the U.S. invasion of Iraq. The war was deeply unpopular among the Turkish public. Erdogan's center-right AKP had only recently come to power, and the vote laid down a new marker in relations between the United States and Turkey, two countries that represented NATO's first and second largest armies.

More than a decade later, and the AKP remains in power, though it finally lost its parliamentary majority in landmark elections last month. During this time, the United States has not been allowed to run bombing sorties from Incirlik, though it has launched unmanned surveillance missions.

Turkey's apparent pact with the White House to allow Incirlik to come into play also signals the expanding dimension of the Syrian war. Reports on Friday evening indicated Turkish fighter jets had also struck at PKK positions in northern Iraq, as the decades-old conflict between Kurdish guerrillas and the Turkish state appears to be lurching back to life.

Meanwhile, Turkish police carried out a massive roundup of 250 suspected Islamic State and PKK militants across the country. The two factions are vastly different: one is a fundamentalist, Sunni extremist outfit; the other an ethnic-nationalist organization built on staunchly secularist, Marxist-Leninist lines. But Turkish authorities do not believe one group is worse than the other.

"The raids are consistent with Turkey’s public comments about viewing the PKK and ISIS as equal threats," Aaron Stein, a Turkey expert at the Atlantic Council's Rafik Hariri Center for the Middle East, told Bloomberg.

That's not a view shared in Washington. After all, last year, the United States had airdropped weapons to Syrian Kurdish factions affiliated to a political party that some in Turkey deem "worse" than the Islamic State. Kurdish factions in Syria and northern Iraq, including PKK units, have proved some of the most reliable frontline fighters against the jihadists.

So while the agreement over Incirlik heralds a new phase of U.S.-Turkish cooperation, it may also reflect the spiraling, expanding nature of a very messy regional conflict.