Despite saying he's working with Democrats amidst the partial federal government shutdown, President Donald Trump is holding a border security meeting with Republican attendees only.

Reports about the shutdown are "mostly fake," he said on Twitter.

The shutdown occurred at midnight EST after the House and Senate adjourned without a federal-spending deal — the result of Trump's last-minute demands for money to fund a wall along the US-Mexico border.

It's unclear how long the shutdown will last, but Trump said he's prepared for a long one.

The partial federal government shutdown that began at midnight EST Saturday may be a long one, warned President Donald Trump, despite calling most of the reports on the matter "FAKE" on Twitter.

Together, his Tweets read:

"I am in the White House, working hard. News reports concerning the Shutdown and Syria are mostly FAKE. We are negotiating with the Democrats on desperately needed Border Security (Gangs, Drugs, Human Trafficking & more) but it could be a long stay. On Syria, we were originally going to be there for three months, and that was seven years ago - we never left. When I became President, ISIS was going wild. Now ISIS is largely defeated and other local countries, including Turkey, should be able to easily take care of whatever remains. We're coming home!"

Read more: 'Mr. President, dig in': Lindsey Graham praises Trump's refusal to compromise over border wall funding even as the government shuts down

But despite saying that he's working with Democrats, none are attending the border security lunch being held Saturday, according to CNN congressional correspondent Phil Mattingly.

Mattingly recently Tweeted out the full list of attendees, all of whom are Republican:

President Donald J. Trump

Vice President Mike Pence

Acting Chief of Staff, Mick Mulvaney

Assistant to the President, Jared Kushner

Assistant to the President, Shahira Knight

Senator Mike Lee

Senator Lindsey Graham

Senator Richard Shelby

Representative Mark Meadows

Representative Jim Jordan

Representative Matt Gaetz

Representative Andy Biggs

When asked about the absence of Democrats in the meeting during a conference call with reporters, a senior administration official said "This president has all sorts of conversations and all sorts of meetings — that doesn't change from day to day." The official would not confirm or deny whether or not Democrats had been invited, simply saying, "in this situation it’s important for Democrats to come forward and put forth options that further the negotiations."

The shutdown occurred after the House and Senate adjourned without a federal-spending deal, the result of Trump's last-minute demands for $5 billion to fund border security, including a wall along the US-Mexico border.

Trump originally supported a short-term funding extension, but the turnaround left Congress with little time to reach a compromise.

It's unclear how long the reported shutdown will last, but it will force 800,000 federal workers to go without pay throughout its duration. Many lawmakers are anticipating a long-term shutdown until a deal is reached that would pass both chambers of Congress and get Trump's signature.

Last week, Trump said he would be "proud" to shut the government down over the border wall fight, and he told reporters earlier in the day on Friday that a government shutdown could last for a long time.

"I hope we don't, but we are totally prepared for a very long shutdown," Trump said during a meeting in the Oval Office.

Fox News' Chad Pergram reports that multiple senior House Republicans don't believe there will be a resolution to the shut down until at least Dec. 27, leaving some workers without pay for nearly a week.

Benjamin Goggin contributed reporting to this article.