UPDATE 2-Trump attacks Washington Post, calls it Amazon's 'chief lobbyist'

(Rewrites, adds background on Trump tweet)

WASHINGTON, April 5 (Reuters) - U.S. President Donald Trump called the Washington Post the "chief lobbyist" for Amazon.com Inc on Thursday, repeating his unsubstantiated attack on the newspaper.

The newspaper is privately owned by Jeff Bezos, the founder and chief executive officer of the online retailer. Amazon does not own the Post.

Trump regularly lashes out against what he perceives as critical articles in the Post as well as the New York Times and CNN. On Thursday he took issue with a story headline in the Post on China retaliating with trade penalties against U.S. products.

"The Fake News Washington Post, Amazon's 'chief lobbyist,' has another (of many) phony headlines," Trump said on Twitter.

Amazon and the Washington Post did not immediately respond to requests for a comment.

Last weekend Trump called the Washington Post a lobbyist for Amazon in a tweet. Martin Baron, the Washington Post's executive editor, rejected the accusation.

"There isnt anybody here who is paid by Amazon," Baron told the New York Times in a report published on Tuesday. "Not one penny."

Amazon shares were up 2.1 percent on Thursday. Before the open, the stock had dropped 4 percent since news website Axios reported last week that Trump was obsessed with Amazon and wanted to curb its power, possibly with antitrust action.

Trump followed that report by repeatedly attacking Amazon's use of the United States Postal Service, claiming it is losing money delivering Amazon packages, without presenting any evidence to back up his assertion. (Reporting by Washington newsroom; Editing by Chizu Nomiyama and Jeffrey Benkoe)