PHNOM PENH, Cambodia — A newspaper widely seen as the last bastion of a free press in Cambodia has been sold to a Malaysian investor with ties to Cambodia’s strongman prime minister, a move that critics say further highlights the country’s slide toward outright authoritarianism.

The English-language newspaper, The Phnom Penh Post, reported the sale on Sunday. The investor, Sivakumar S. Ganapathy, is the chief executive of a public relations firm that has worked on behalf of Prime Minister Hun Sen.

Intervention in the paper’s editorial decision making came almost immediately after the sale was announced. Several senior editors resigned or were fired after they refused to excise a story from the paper’s website about the relationship between Mr. Sivakumar’s firm and the Cambodian government.

The sale comes about seven months after the government forced The Post’s longtime rival, The Cambodia Daily, to close over allegations that it had not paid millions of dollars in taxes, and two months before a general election. The Post itself had owed $3.9 million in taxes, but that bill was settled as part of the sale, The Post reported.