U.S. Customs treated Oscar-nominated Palestinian director Emad Burnat like a NATIONAL THREAT last night at LAX -- putting him and his family in an isolated room and ordering him not to use his cell phone -- so says the director ... but law enforcement says he's exaggerating.

You'll recall ... Burnat's friend Michael Moore flipped out while Burnat was detained at the airport, tweeting like mad about the injustices of U.S. Customs and Border Protection ... and today, Burnat joined us on TMZ Live to discuss his experience.

Burnat -- whose documentary "5 Broken Cameras" is up for an Academy Award -- told us, he was stopped by immigration upon his arrival in the States ... and what followed was nightmarish.

Burnat says the customs officers did not believe him when he told them he was an Academy Award-nominated director ... so they put him and his family into an isolated room to question them, threatening to deport them back to Palestine.

Burnat says he tried to show the agents the email he received from the Academy -- which contained his Oscar invite -- and even tried to show his hotel reservation ... but they weren't having it.

When he tried to text and email friends for help, Burnat says he was instructed not to use his phone. Luckily, Burnat says he was able to slip a message to Michael Moore informing Michael of the situation ... and Michael sounded the alarms, notifying Academy officials who then contacted their lawyers.

Burnat says he was detained for roughly an hour-and-a-half total -- and when he was finally released, he was never given an apology.

But law enforcement sources tell TMZ ... Burnat is embellishing the story ... and that he was only sent to a secondary screening area simply to answer questions ... and was only detained for 25 minutes, total.

We raised the issue with Burnat -- but he's adamant, he was mistreated.