Julie Hamp, Toyota's highest-ranking female executive, pictured on April 3, 2015, has resigned after she was taken into custody for importing a controlled substance without permission (AFP Photo/)

Tokyo (AFP) - Japan's Toyota Motor said Wednesday that American Julie Hamp, its most senior female executive, has resigned after being arrested for suspected drug law violations.

"Toyota Motor Corp (TMC) received notification from Ms. Julie Hamp of her intent to resign her position of managing officer," the company said in a statement dated Tuesday.

"TMC has accepted her resignation after considering the concerns and inconvenience that recent events have caused our stakeholders."

Hamp, who was recently appointed to head global public relations at the world's biggest carmaker, was taken into custody last month for importing a controlled substance without permission.

She remains in custody, under laws that allow a suspect to be held for up to 23 days without charge.

She was arrested at her Tokyo hotel after a package containing oxycodone was intercepted at Narita airport.

Oxycodone -- an opioid used to relieve pain -- is legal with a prescription, but importing it without permission from the authorities is illegal and could be punished by up to 10 years in prison.

The 55-year-old Hamp told prosecutors she had the powerful painkiller shipped from the United States to ease problems with her knees.

Hamp "said she did not believe she had imported narcotics when she was arrested", a police official has said.

The parcel was sent to Hamp on June 8 from the US and arrived at Tokyo's Narita airport on June 11 where it was intercepted, according to police.

The package, labelled "necklaces", contained several small boxes, each holding accessories and several tablets, reports have said, adding that police suspect there had been an attempt to hide the drug.

Subsequent reports have said her father had posted the package to her.

Oxycodone, which can be addictive, is designated as a narcotic in Japan but can be prescribed by a doctor to relieve pain.

Japanese law allows individuals to bring the drug from abroad if they have a legitimate prescription. However it cannot be sent by mail.

"Because the investigation of Ms. Hamp is ongoing, there is little Toyota can say at this time," the firm said in Wednesday's statement.

"We remain firmly committed to putting the right people in the right places, regardless of nationality, gender, age and other factors," it said.

After her arrest, Toyota's chief executive Akio Toyoda apologised and pledged his support for Hamp, who in April became the company's first non-Japanese executive posted to work permanently in Toyota's home market.

"We believe it will become clear that Ms Hamp did not intend to break the law... Ms Hamp is a dear colleague whom I trust," Toyoda said.