The US provided Turkey with intelligence, including surveillance video and information from reconnaissance aircraft, that may have aided in its assault on the US-allied Kurdish forces in Syria, The New York Times reported.

The intelligence sharing continued as late as Monday — two days before Turkey invaded Syria to go after the Kurds — according to the report.

Past reports suggest the US in 2017 began sharing more intelligence on the Kurds with Turkey to quell the Turkish government's anger over Trump arming Kurdish forces in Syria.

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The US provided Turkey with intelligence that may have helped it track and target Kurdish forces in Syria that played a vital role in the US-led fight against ISIS, The New York Times reported on Wednesday.

The US was providing intelligence to Turkey on the region as part of a counterterrorism partnership up until Monday, a Department of Defense official told The Times, the day after the Trump administration announced it was pulling US troops from northeastern Syria ahead of a Turkish operation.

Trump's decision to pull US forces from the region has been broadly criticized as a betrayal of the Kurds and a green light for a Turkish military operation, though the president disputes this.

Turkish President Recep Tayyip Erdogan announced the onset of a military operation against the US-allied Kurdish forces in Syria on Wednesday. The early part of the assault involved air strikes in at least five towns along the Turkey-Syria border, and within hours, Turkish ground troops crossed into Syria. After the incursion began, Trump said the US did not endorse it and that it was a "bad idea."

Read more: Trump defends abandoning the Kurds by saying they didn't help the US in WWII

Two US officials told The Times that as Turkish military officials planned the assault over the past few weeks, they were provided with American surveillance video and information from reconnaissance aircraft. Information like this could prove useful in picking out targets for air strikes.

The White House declined to comment when contacted by Insider on this matter, and the Department of Defense did not immediately respond to a request for comment.

Turkey is a NATO ally to the US, and in this capacity, it's not unusual for intelligence sharing to occur. In 2016, NATO created an intelligence-chief post with a specific emphasis on increasing intelligence coordination between member states on counterterrorism efforts — particularly against ISIS. Trump, who was a presidential candidate at the time, took credit for this.

But the intelligence sharing between the US and Turkey has also, in the past, been specifically tied to Ankara's, Turkey's capital, consternation about the Kurds, highlighting the convoluted nature of the relationship between the two countries.

A quick rundown on the complex dynamics between the US, the Kurds, and Turkey, and how this relates to intelligence sharing:

The Kurds are a distinct ethnic group with an estimated population of up to 35 million occupying a region straddling the borders of Turkey, Syria, Iran, Iraq, and Armenia. The Kurds have never had a permanent or official nation state.

The fraught history of the Kurds can largely be traced back to World War I and the collapse of the Ottoman Empire. Their lack of a central homeland has fostered major tensions with Turkey over the years.

The US alliance with the Kurdish-led Syrian Democratic Forces (SDF) dates back to 2015 under the Obama administration.

The SDF is an alliance of militias in the region that bore the brunt of the US-led campaign against ISIS and lost about 11,000 fighters in the process. It played a crucial role in dismantling ISIS's so-called caliphate.

But the US's alliance with the Kurdish forces has also been a continuous source of tension in terms of its relationship with Turkey, a fellow NATO member.

In May 2017, Trump angered Turkey after he approved a plan to arm the Syrian Kurdish People's Protection Units (YPG) — the dominate fighting force in the SDF — in the campaign against ISIS.

Turkey views the YPG as a terrorist organization and a threat to its borders, so Erdogan responded to the move by accusing the US of siding with a terrorist organization.

Turkey felt Trump arming the YPG empowered the Kurdistan Workers' Party (PKK), a group the US and Turkish governments both consider a terrorist organization.

The PKK has waged a violent separatist campaign against the Turkish government since the 1980s, with the broader goal of establishing an independent Kurdish state within Turkey.

The YPG, which has been active since 2004, also has ambitions of establishing an autonomous state for the Kurdish people.

The YPG has denied any explicit or direct organizational links with the PKK, and the US does not view the YPG as a terrorist entity.

But in Turkey's eyes, the YPG and PKK are virtually synonymous, which is why it was livid Trump armed the former.

In an effort to quell Turkey's anger over Washington's alliance with the YPG, the US in May 2017 moved to increase intelligence cooperation to help Ankara go after the PKK, according to reports from The Wall Street Journal and Reuters.

At the time, then-Defense Secretary James Mattis said, "We agree 100% with Turkey's concern about PKK ... and we support Turkey in its fight against PKK as a fellow NATO member."

But Turkey did not let the issue go in the time since, and Erdogan continued to make clear his desire to go after Kurdish forces across the border in Syria. The fight against ISIS, and presence of US troops in the region, however, presented a major roadblock to this until Trump decided to remove it.

Months ago, Trump said he stopped Erdogan from wiping out the Kurds in Syria, but now he's stepped aside.

At a June press conference in Japan, the president spoke about the ongoing tensions with Erdogan over the Kurds and suggested he was standing in the way of a massacre.

"Frankly, he wanted to wipe out — he has a big problem with the Kurds, as everyone knows," Trump said at the time. "And he had a 65,000-man army at the border, and he was going to wipe out the Kurds, who helped us with ISIS."

"And I called him and I asked him not to do it. They are, I guess, natural enemies of his or Turkey's. And he hasn't done it," Trump said. "They were lined up to go out and wipe out the people that we just defeated the ISIS caliphate with, and I said, 'You can't do that.' You can't do it. And he didn't do it."

Read more: Trump's Syria retreat is a massive break from post-9/11 Republicanism

But after a call between Erdogan and Trump on Sunday, the White House announced the US was removing troops from the region. It paved the way for the Turkish assault on the Kurds there several days later.

The SDF has called Trump's decision a "stab in the back," and US lawmakers, including Republicans, excoriated the president. Beyond their anger over Trump abandoning the Kurds, the lawmakers are concerned the move will lead to the resurgence of ISIS in the region while creating a security vacuum that benefits US adversaries such as Russia and Iran.

Kurdish forces have been detaining thousands of ISIS fighters but are now solely focused on responding to the Turkish operation, and that opens the door for the imprisoned terrorists to escape. Trump dismissed concerns about this on Wednesday, saying that the ISIS fighters would be "escaping to Europe."

Meanwhile, as Trump continues to defend his decision, Erdogan on Thursday morning boasted that over 100 "terrorists" had been killed in the operation thus far.