President Donald Trump at the Ford's Theatre Gala, an annual charity event to honor the legacy of President Abraham Lincoln, in Washington on Sunday. REUTERS/Mike Theiler President Donald Trump on Monday doubled down on his executive order banning travel to the US from six majority-Muslim countries after the terror attack in London on Saturday night.

"People, the lawyers and the courts can call it whatever they want, but I am calling it what we need and what it is, a TRAVEL BAN!" Trump said in the first of a series of tweets Monday morning.

Trump went on to attack the US courts, which have blocked the order from being carried out, and suggested the Department of Justice should have fought harder to retain an earlier version of the order, which critics said unconstitutionally targeted Muslims.

"The Justice Dept. should have stayed with the original Travel Ban, not the watered down, politically correct version they submitted to S.C.," the president continued Monday.

"The Justice Dept. should ask for an expedited hearing of the watered down Travel Ban before the Supreme Court — & seek much tougher version!" Trump said.

A petition by the Department of Justice last week asked the Supreme Court's nine-justice panel to rule on the legality of Trump's order. In a May ruling halting the order, the 4th US Circuit Court of Appeals argued that the travel ban "drips with religious intolerance, animus, and discrimination."

The Trump administration had vowed to take the case to the Supreme Court since the earlier version of Trump's executive order on travel was slapped down by the San Francisco-based 9th US Circuit Court of Appeals in February.

Trump's Monday tweets could complicate the DOJ's legal case, as the department has tried to distance the revised order from the earlier version.

The White House initially tried to reframe Trump's use of "travel ban" when the executive order was first announced in January.

The White House press secretary, Sean Spicer, said in January that the policy was not a ban but rather "extreme vetting." But Spicer referred to it as a travel ban as recently as May.

Trump used similar language over the weekend, tweeting after the Saturday-night terrorist attack in London.

"We need to be smart, vigilant and tough," Trump tweeted. "We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety."

During his tweetstorm Monday morning, Trump called the court system "slow and political."

"In any event we are EXTREME VETTING people coming into the U.S. in order to help keep our country safe," Trump tweeted. "The courts are slow and political!"

Bryan Logan contributed reporting to this story.