The Duchess of Sussex’s estranged half-brother, Thomas Markle Jr, has been named as a “person of interest” in the Philippine authorities’ inquiry into child sexual abuse image allegations made against her father, Thomas Markle Sr.

The country’s interior and local government secretary, Jonvic Remulla, told a press conference in Manila there were “signs that point that the son is involved in the crime as well”.

He added that Markle Jr, 60, who alerted local police and the FBI to images he found in his father’s belongings, was not yet being treated as a suspect. His alleged involvement is not thought to be directly linked to the material he handed to the police.

More than 7,000 photos and one video – all of under-age males and females of Asian, Latin and European descent, with some as young as 10 and 11 – were uncovered, Remulla said.

He described the images as “the most deplorable displays of impunity towards sexual activity that I have ever seen”.

Markle Sr, 82, who is estranged from Meghan, has reportedly been moved into a care home for dementia patients in the US where he is now living.

Remulla said: “We’re determining if [the] son is involved … There are signs that point that the son is involved in the crime as well but only as a person of interest so far.”

He added: “We will know in the next few days.”

Markle Sr, who returned to the US from the Philippines in May, has admitted paying for sex in the Philippines but he has strongly denied possessing child abuse imagery, and suggested he had been “set up”. His son remains in Cebu City in the Philippines.

Remulla has previously described Markle Sr as “a possible sex offender of the grossest kind”.

Markle Jr reported his father after claiming to have found four storage boxes at his father’s home in the Philippines containing “hundreds, if not thousands” of child sex abuse images.

Police and FBI agents have since been investigating whether Markle Sr was in possession of any illegal images while living in the Philippines and in Mexico, where he previously lived, and where other illegal images were reportedly found in one of his storage units.

Markle Jr was recently interviewed at his home in Cordova, Cebu, as part of an international, multi-agency meeting via Microsoft Teams, according to the Sun, which first published the claims. He gave his statement to an FBI agent based in Florida, who specialises in child sex abuse cases.

In a statement issued when the allegations against her father were first published, Meghan said she was “deeply distressed” by the claims. She said she had been informed of disturbing allegations against her father in 2018 and had kept him from having contact with her children, Prince Archie, seven, and Princess Lilibet, five, to protect them.