The United States on Tuesday announced that it would supply weapons and military equipment to Kurdish fighters battling ISIL in Syria, despite intense opposition from NATO ally Turkey.
Dana White, the Pentagon's chief spokeswoman, said in a written statement that US President Donald Trump had authorised the arms shipments on Monday.
She said Trump's approval gave the Pentagon the go-ahead to "equip Kurdish elements of the Syrian Democratic Forces [SDF] as necessary to ensure a clear victory" over ISIL in Raqqa, the armed group's self-declared capital in Syria.
The Kurdish elements of the SDF are from the Kurdish People's Protection Units (YPG) and they have been the main faction fighting ISIL, which stands for Islamic State of Iraq and the Levant, and is also known as ISIS, on the ground in Syria.
The Pentagon statement said they are "the only force on the ground that can successfully seize Raqqa in the near future".
But Turkey says YPG fighters are linked to Kurdistan Workers' Party (PKK) separatists inside Turkey, who have waged an armed campaign since 1984 that has killed more than 40,000 people.
There was no immediate reaction from Turkish officials, but the move is expected to anger Ankara which considers the Kurdish forces to be "terrorists".
"The Turks are going to be unhappy with this because, in no way, they want to see any kind of bolstering of strength of Kurdish forces in that area," Al Jazeera's Charles Stratford, reporting from Gaziantep on the Turkish side of the Syria-Turkey border, said.
"The SDF now are saying that after Raqqa they want to push further south to take Deir Az Zor ... [and the] Trump administration's reaffirmed support is no doubt going to upset the Turks very much."
The Pentagon's announcement comes before a scheduled meeting between Turkish President Recep Tayyip Erdogan and Trump in Washington next week.
Speaking to Al Jazeera last month, Erdogan criticised Trump's predecessor, Barack Obama, over an agreement between the two to fight what he described as "terrorist groups" operating in Turkey.
"With President Obama, we had a mutual agreement about the PKK - but Obama deceived us. I don't believe the Trump administration will do the same," Erdogan said.
"The YPG is an arm of the PKK. We must put an end to this," he added.
"We can't destroy one terrorist group with another one. We are strategic partners with the US."
While the Pentagon's statement did not mention the kinds of arms to be provided to the Kurds, other officials had indicated in recent days that 120mm mortars, machineguns, ammunition and light armoured vehicles were possibilities. They said the US would not provide artillery or surface-to-air missiles.
As many as 1,000 US troops are working alongside the SDF inside Syria.
Senior US officials including General Joseph Dunford, chairman of the Joint Chiefs of Staff, have met repeatedly with Turkish officials to try to work out an arrangement for the Raqqa assault that would be acceptable to Ankara.
Ankara has insisted that the Syrian Kurds be excluded from that operation, but US officials said there was no real alternative.
In her statement, White, the Pentagon spokeswoman, said the US prioritises its support for the Arab elements of the SDF.
"We are keenly aware of the security concerns of our coalition partner Turkey," she said.
"We want to reassure the people and government of Turkey that the US is committed to preventing additional security risks and protecting our NATO ally."
Other officials said Trump's authorisation includes safeguards intended to reassure Ankara that the additional US weaponry and equipment will not be used by the Kurds in Turkey.
The intent is to restrict the distribution and use of the weaponry by permitting its use for specific battlefield missions and then requiring the Kurds to return it to US control.
The decision to arm the Kurds was announced just hours after James Mattis, the Pentagon chief, met a Turkish official in Denmark at an anti-ISIL coalition summit.
Mattis sounded upbeat on the relationship with Turkey, but it was not clear if the arming of the Kurds had come up in the discussion.
The Pentagon chief said he had useful discussions with Turkey and described the two countries as working out differences over the US' alliance with Syrian Kurds.
Source: Al Jazeera and news agencies