Announcement comes as Trump says that US forces will withdraw from neighbouring Syria
The United States said on Wednesday it has approved the sale of $3.5bn in missiles to Turkey, in an overture to Ankara following US outrage over the NATO ally's plans to buy weapons from Russia.
The announcement came as President Donald Trump said that US forces would withdraw from neighbouring Syria, a decision likely to please Turkey as it pursues Kurdish fighters.
The State Department said it had informed Congress of plans to sell Turkey a package that includes 80 Patriot missiles, 60 PAC-3 missile interceptors and related equipment.
"The proposed sale will increase the defensive capabilities of the Turkey military to guard against hostile aggression and shield NATO allies who might train and operate within Turkey's borders," a statement said.
Russia and Turkey have already concluded a deal for Ankara to buy the rival Russian S-400 system, with deliveries expected to begin next year despite warnings from the US and NATO member countries.
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Speaking to reporters on a conference call, Kremlin spokesman Dmitry Peskov said that the Russian and US transactions should be seen as separate from each other and that Russia was in the process of fulfilling the terms of the deal to supply Ankara with S-400s.
A State Department official said that Turkey is jeopardising participation in another US military programme, new F-35 fighter jets, if Ankara goes ahead with the S-400 sale.
Turkey may also face sanctions on defence purchases under US law if the Russia purchase is completed, the official said on condition of anonymity.
A purchase from Russia "would have serious ramifications for US ability to do business with Turkey across the defence-trade spectrum," the official said.
The announcement came as Trump said that the US had defeated the Islamic State (IS) group in neighbouring Syria - leading to the withdrawal of US troops, who had effectively protected Kurdish fighters against Turkey.
There was no immediate indication that the two announcements were linked, but Trump has made clear that arms sales are a top priority - citing the income from weapons in defending US ties with Saudi Arabia after the kingdom's killing of Saudi journalist Jamal Khashoggi in Istanbul.
Turkish President Recep Tayyip Erdogan on Monday vowed to "remove" the Kurdish fighters if necessary, adding that he had spoken by telephone with Trump and agreed to cooperate in Syria.
Erdogan has called the US-backed Kurdish forces "terrorists," linking them with the Kurdish Workers' Party, or PKK, which has waged an insurgency inside Turkey in the name of the Kurdish minority since 1984.
Turkey had until now been forced to be more hesitant in targeting the Kurdish forces, knowing that casualties among US troops would trigger a crisis.
Turkish Foreign Minister Mevlut Cavusoglu said on Sunday that Trump had also promised to look at another priority for Erdogan - extraditing Fethullah Gulen, an influential cleric in exile in Pennsylvania whom the Turkish leader accuses of plotting a failed 2016 coup against him.
Trump had piled pressure on Erdogan and imposed sanctions over the detention of an evangelical US pastor, Andrew Brunson. He was released in October, removing a major impediment in relations.