British Police say they are investigating a racist hate crime after a suspicious package was sent to Meghan Markle sparking an anthrax scare.

Police said the letter was received on February 12 at London’s St James’s Palace containing a white powder later found to be harmless.

UK media quoted police sources as saying the package was addressed to Meghan and contained a racist note.

In a statement, Scotland Yard said: “Officers are also investigating an allegation of malicious communications, which relates to the same package, and it is being treated as a racist hate crime.”

“The matter is being investigated by officers from the Met’s counter-terrorism command,” it said.

Meghan, whose mother is African-American, will marry Prince Harry in May.

In a public rebuke from his office to the media in 2016 over intrusion into his fiancée’s private life, Harry referred to the racism that had been directed at Meghan.

Asked about the scrutiny of her ethnicity in a TV interview after their engagement was announced, Meghan said: “Of course it’s disheartening, you know it’s a shame that that is the climate in this world to focus so much on that.”

St James’s Palace contains state apartments and offices used by Prince Charles, Prince William, Harry and other royals.

Prince Charles’s official London residence, Clarence House, is next to the palace, while his sons, William and Harry, live at Kensington Palace, about 1.5 kilometres away.

“Police are investigating after a package containing a substance was delivered to St James’s Palace on Monday 12 February,” Scotland Yard said.

“The substance was tested and confirmed as non-suspicious. Officers are also investigating an allegation of malicious communications, which relates to the same package. No arrests; inquiries continue.”

A spokesperson for St James’s Palace said they would not comment and it was a matter for the police.

The police investigation follows a similar scare after a package containing harmless white powder was delivered to an office in the British parliament in central London on February 13.

Unconfirmed British media reports said that package was addressed to Home Secretary Amber Rudd.

The police did not say if they believe the two incidents are linked.

– With AAP