WASHINGTON (Reuters) - The Department of Justice's antitrust chief, Makan Delrahim, said on Tuesday that evidence drove the division's decision-making rather than pressure from the president, who recently tweeted that he supported an antitrust probe of Comcast Corp CMCSA.O.

FILE PHOTO - A U.S. flag flies at the headquarters of the Department of Justice in Washington, U.S., August 3, 2018. REUTERS/Brian Snyder

Speaking on CNBC, Delrahim, the assistant attorney general for antitrust, was asked about President Donald Trump's attacks on companies like Comcast and Amazon.com Inc AMZN.O, alleging that they break antitrust law.

“As far as what we do in our enforcement -- we need the evidence, we need the economics, (before) we go to court. Politics that goes on between various aspects of the government don’t affect our decisions to make these cases,” Delrahim said.

The DOJ’s Antitrust Division cannot order the halting of a merger or breaking up of a company, but must convince a judge that such an action is needed. The department failed this year to convince a federal judge to stop AT&T’s merger with Time Warner and is appealing that loss.

Delrahim said the division was “vigilant” in monitoring Comcast since a consent decree expired that governed its purchase with NBC Universal.

Trump tweeted support on Monday for the American Cable Association’s call for an investigation into Comcast. “They say that Comcast routinely violates Antitrust Laws,” he wrote.

Delrahim said concern over Amazon was “bipartisan,” but added that the fact that a company was big and powerful did not mean that it broke antitrust law.

Trump had tweeted about his unhappiness with Amazon in July, saying: “In my opinion the Washington Post is nothing more than an expensive lobbyist for Amazon.” Amazon chief Jeff Bezos also owns the Washington Post.

Delrahim seemed unfazed by the unusually high level of attention paid to the work of his division.

“I think it’s great that we have such a debate about free markets. And the antitrust laws (are) there to protect the free markets,” he said.