U.S. immigration authorities are barring entry to a 21-year-old Syrian cinematographer who worked on a harrowing film about his nation's civil war, The White Helmets, that has been nominated for an Academy Award.

According to internal Trump administration correspondence seen by The Associated Press, the Department of Homeland Security has decided at the last minute to block Khaled Khatib from travelling to Los Angeles for the Oscars.

Khatib was scheduled to arrive Saturday in Los Angeles on a Turkish Airlines flight departing from Istanbul. But his plans have been upended after U.S. officials reported finding "derogatory information" regarding Khatib.

Derogatory information is a broad category that can include anything from terror connections to passport irregularities. Asked for comment, a spokeswoman for the Department of Homeland Security, Gillian Christensen, said, "A valid travel document is required for travel to the United States."

The White Helmets, a 40-minute Netflix documentary, has been nominated for Best Documentary Short. If the film wins the Oscar, the award would go to director Orlando von Einsiedel and producer Joanna Natasegara. Khatib is one of three people credited for cinematography; Franklin Dow is the film's director of photography.

The film focuses on the rescue workers who risk their lives to save Syrians affected by civil war. Many of the group's members have been killed by Syrian President Bashar Assad's air forces.

The group also was nominated for last year's Nobel Peace Prize.

The White Helmets includes emblematic scenes of the deadly six-year-old conflict: people digging through destroyed homes looking for survivors, at constant risk of "double tap" attacks that target first responders after they've arrived at the scene of a strike.

Khatib had been issued a visa to attend the ceremony with Hollywood's biggest stars. But Turkish authorities detained him this week, according to the internal U.S. government correspondence, and he suddenly needed a passport waiver from the United States to enter the country. The correspondence indicated he would not receive such a waiver. There was no explanation in the correspondence for why Turkey detained Khatib.

Reached by telephone, Khatib said he was currently in Istanbul and had not been detained. He declined to speak further about his situation.

Jodie Foster, Michael J. Fox at unity rally

The barring of Khatib comes immediately after celebrities and top talent agents gathered in Beverly Hills, Calif., for a different kind of pre-Oscars event: a rally for immigration rights.

Jodie Foster, Michael J. Fox and Keegan-Michael Key were among the speakers at Friday's rally, organized by the United Talent Agency outside its Beverly Hills headquarters. The talent agency, better known as UTA, planned the nearly two-hour United Voices rally in lieu of holding its annual Oscars party. Security officials estimated there were 1,200 people in attendance.

New immigration policies an 'assault on human dignity,' says Michael J. Fox2:38

Key, who kicked things off, said the event was intended to "support the creative community's growing concern with anti-immigration sentiment in the United States of America and its potential chilling effect on the global exchange of ideas, not to mention freedom of expression."

He welcomed all, including a handful of Trump supporters, because "this is America, where you get to believe what you want."

For the most part, however, the crowd was subdued, civil and attentive to the celebrity speakers. Canadian Michael J. Fox, who became a United States citizen some 20 years ago, remembered being annoyed at the eight-year process to citizenship and now wonders what he was complaining about.

Turning immigrants away, Fox said, is an "assault on human dignity."

'It's time to show up:' Jodie Foster speaks at unity rally3:44

One of the best-received was an enthusiastic Jodie Foster, who said she's never been comfortable using her public face for activism and has always found the small ways to serve, but that this year is different.

"It's time to show up," she said. "It's a singular time in history. It's time to engage. And as the very, very dead Frederick Douglass once said, 'Any time is a good time for illumination."'

UTA previously announced that it was donating $250,000 US to the ACLU and the International Rescue Committee and has set up a crowdfunding page to solicit more donations. It has raised over $320,000 US. ​

'I hope this unity will continue:' Farhadi

Oscar-winning Iranian filmmaker Asghar Farhadi spoke via video from Tehran to praise the show of unity among the cinema community. Farhadi, nominated anew this year for The Salesman, previously said he would boycott Sunday's ceremony as a result of U.S. President Donald Trump's travel ban.

"It is comforting to know that at a time when some politicians are trying to promote hate by creating divisions between cultures, religions and nationalities, the cinema community has joined the people in a common show of unity to announce its opposition," Farhadi said.

"I hope this unity will continue and spread to fight other injustices."

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Filmmaker Asghar Farhadi won Iran's first-ever Oscar in 2012 for his drama A Separation. Though nominated again for The Salesman, he is boycotting the ceremony to protest U.S. President Donald Trump's travel ban. (Jason Merritt/Getty Images)

He and the other directors nominated for this year's best foreign-language film Oscar also issued a statement condemning "the climate of fanaticism and nationalism we see today in the U.S. and in so many other countries, in parts of the population and, most unfortunately of all, among leading politicians."

The directors added that regardless of who wins on Sunday, "we believe there is no best country, best gender, best religion or best colour. We want this award to stand as a symbol of unity between nations and the freedom of the arts."