Altaf Ahmad Shah, a prominent politician from Kashmir who campaigned against India's rule over the region, has died in police custody, his family said on Tuesday. He was 66 years old.

Indian authorities arrested the Kashmiri separatist along with six others in 2017 in a "terror-funding case." This year, he was diagnosed with cancer while in custody.

The Hindu newspaper reported that authorities had not yet confirmed the cause of death.

On Tuesday, Shah's daughter Ruwa tweeted that he took his last breath "as a prisoner."

Pakistani Prime Minister Shahbaz Sharif said he too was "deeply grieved" by Shah's death.

"Custodial killings are the norm in Modi's India," he added.

Medical treatment criticized

Shah was diagnosed with kidney cancer in September.

After public pleas from his family, he was relocated to the Dr. Ram Manohar Lohia Hospital in New Delhi.

However, Shah later said in court that the hospital did not have adequate facilities to treat renal cancer, the Press Trust of India reported. His daughter also accused Indian authorities of placing him in an ill-equipped medical center.

After the Delhi High Court intervened to ensure Shah received "appropriate treatment," the Kashmiri leader was again moved, this time to the All India Institute of Medical Sciences, India's premier healthcare facility.

On Tuesday, after Shah's death, Pakistani Prime Minister Sharif said the "Modi regime denied him treatment despite knowing he was a cancer patient."

Crackdown on Kashmir separatists

Shah is the fourth separatist leader from India-controlled Kashmir to have died in police custody in the last three years.

He was part of Tehreek-e-Hurriyat, an anti-India political group that supported calls to merge Kashmir into Pakistan.

In 2020, Indian authorities also imprisoned the group's chairman Muhammad Ashraf Sehrai. The party leader died in custody last year aged 77.

This report was written in part with material from the Associated Press.

Edited by: Rebecca Staudenmaier