Turkey is to let the US carry out airstrikes against the Islamic State group from a key military base near the Syrian border, US officials have said.
The agreement, yet to be confirmed by Ankara, follows months of negotiations.
The deal comes after Turkey and IS fighters exchanged fire near the Turkey-Syria border, with one soldier killed and two more injured.
On Monday, 32 people were killed in a suicide attack in a Turkish town on the Syrian border blamed on IS.
The agreement was finalised in a phone call between President Barack Obama and his Turkish counterpart Recep Tayyip Erdogan on Wednesday. It was confirmed by US officials speaking on condition of anonymity.
The use of the Incirlik airbase broadens the US military’s ability to strike IS targets – one US official told the New York Times it was a “game changer”.
Once used in raids against former Iraqi leader Saddam Hussein, the base is near to Turkey’s long border with Syria, and significantly narrows the distance to the IS stronghold of Raqqa.
Analysis: Guney Yildiz, BBC News
This agreement goes beyond providing the US-led coalition against IS with a geographical advantage.
Turkey has been in the coalition since from the beginning but was not fully cooperating due to its differing views over the Syrian crisis.
The Turkish government argued that the first priority of an international coalition should be removing President Assad rather than attacking IS. Having the Turkish government clearly backing the coalition brings extra political clout against IS.
The Turkish government, which has until the beginning of this year been accused of turning a blind eye by allowing IS fighters to cross its borders, was under huge international pressure to open the airbase.
The negotiations between the US and the Turkish government came to fruition as recent attacks by IS against Turkish and Kurdish targets added an urgency to the response.
The White House is yet to comment on the agreement, but White House spokesman Josh Earnest said that Mr Obama and Mr Erdogan had agreed to “deepen our cooperation” in their conversation.
The deal marks a step up in Turkey’s involvement in the campaign against IS.
Ankara has faced criticism at home and abroad for not doing enough against the extremist group, despite being part of the international coalition fighting IS.
Thursday saw a deadly exchange of fire between Islamic State and Turkey near the town of Kilis.
IS fighters attacked a Turkish border post, with the Turkish army retaliating with heavy weaponry, killing one of the militants, Turkish officials said.
The incident comes days after the deadly bombing in the predominantly Kurdish town of Suruc, in which 32 people were killed, mostly university students.
Turkish blamed the attack on IS, with the bomber identified as a 20-year-old believed to have travelled to Syria last year with the help of an IS-linked group.
Kurdish militants said they killed two police officers in the city of Celanpinar as retaliation, accusing the policemen of having retaliated with IS.
Turkey would take “all necessary measures” to protect national security following the attacks, the prime minister’s office said.