President Donald Trump with Turkish President Recep Tayyip Erdogan during the UN General Assembly in New York in 2017. REUTERS/Kevin Lamarque

President Donald Trump reportedly advised Turkey not to invade northeastern Syria and offered to resume sales of the US's fifth-generation aircraft, the Lockheed Martin F-35.

Trump offered Erdogan "a really good package," in addition to other benefits and a presidential visit, a senior official said, according to a Washington Post report published Wednesday.

The purported offer marks a departure from the US's policy since July not to include Turkey in its flagship F-35 program.

The US granted F-35 contracts to several allies, including the UK and South Korea, but took Turkey off that list when it purchased Russia's advanced S-400 air-defense systems.

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In a phone call between President Donald Trump and Turkish President Recep Tayyip Erdogan on Sunday, the US president reportedly advised Turkey not to invade northeastern Syria and offered to resume sales of the US's fifth-generation aircraft, the Lockheed Martin F-35.

Trump offered Erdogan "a really good package," in addition to other benefits and a presidential visit, a senior State Department official told the Washington Post columnist Josh Rogin.

Erdogan is still scheduled to visit the White House in November.

Trump made the decision to withdraw US troops from northeastern Syria near the Turkish border on Sunday following his call with Erdogan. Thousands of US-backed Kurds are stationed in northeastern Syria, and observers say Trump's decision has left the Kurdish fighters vulnerable to Turkish attack and may even fuel an ISIS resurgence.

Turkey has long cited the Kurdish People's Protection Units, or YPG, and the majority-Kurdish Syrian Democratic Forces as terrorist threats with links to the Kurdistan Workers' Party, or PKK. The PKK is a Turkey-based rebel group that has been designated as a terrorist organization by the US and Turkey.

Read more: Trump brushes off worries that freed ISIS prisoners will be a threat: 'They're going to be escaping to Europe'

Israel's first F-35A Lightning II fighter jet being revealed during a ceremony. Lockheed Martin

F-35s or the Russian S-400

Trump's purported offer to Erdogan marks a departure from the US's policy since July not to include Turkey in its flagship F-35 program. The US granted F-35 contracts to several allies, including the UK and South Korea, but took Turkey off that list when it purchased Russia's advanced S-400 air-defense systems.

"The F-35 cannot coexist with a Russian intelligence collection platform that will be used to learn about its advanced capabilities," the White House said in a statement at the time.

"Turkey has been a long-standing and trusted partner and NATO ally for over 65 years, but accepting the S-400 undermines the commitments all NATO allies made to each other to move away from Russian systems," the statement added. "This will have detrimental impacts on Turkish interoperability with the alliance."

Turkey, which created more than 900 parts for the F-35, was removed from the program and is expected to be replaced by American manufacturers by March 2020, according to Lockheed Martin CEO Marillyn Hewson. The country had said it would buy 100 F-35As.

The US also withdrew its offer of a $3.5 billion Patriot missile-system contract over Turkey's purchase of Russia's S-400s.

Turkish officials protested the expulsions and described it as a "mistake which would open irreparable wounds."

Russian S-400 air-defense missile systems in Moscow during the Victory Day parade on May 9, 2018. REUTERS/Sergei Karpukhin

Read more: 'This is just chaos': Retired Marine general condemns Trump's decision to stand down as Turkey launches military attacks in Syria

Despite warnings from Congress, Trump sympathized with Turkey and signaled the resumption of F-35 deliveries. Under the Countering America's Adversaries Through Sanctions Act, Turkey's purchase of Russian military equipment makes it liable to US sanctions.

"It's a very tough situation that they're in, and it's a very tough situation that we've been placed in the United States," Trump told reporters in July. "We'll see what happens. But it's not really fair."

"Because of the fact that you bought a Russian missile, we're not allowed to sell them billions of dollars' worth of aircraft," he added. "It's not a fair situation."

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