Thousands of mourners Friday attended the funeral of Palestinian human rights activist Nizar Banat, an AFP correspondent said, a day after he died in custody following his violent arrest by Palestinian security forces.

The death of the 43-year-old, known for social media videos denouncing alleged corruption within the Palestinian Authority (PA), sparked outrage in the occupied West Bank.

"The people want the fall of the regime," chanted the crowd gathered in the flashpoint West Bank city of Hebron, where Banat was from and where his funeral took place Friday afternoon.

Hebron governor Jibrin al-Bakri said Palestinian security forces arrested Banat in the early hours of Thursday morning, and that "his health deteriorated" while he was in custody.

Banat's family said the forces used pepper spray on him, beat him badly and dragged him away in a vehicle.

Samir Abu Zarzour, the doctor who carried out the autopsy, told reporters on Thursday that injuries on Banat's body indicated he had been beaten on the head, chest, neck, legs and hands.

Less than an hour elapsed between his arrest and his death, Abu Zarzour said.

Banat had registered as a candidate in Palestinian parliamentary elections that were set for May until president Mahmud Abbas postponed them indefinitely.

Palestinian prime minister Mohammad Shtayyeh said an investigation had been launched.

The United States said it was "deeply disturbed" by Banat's death, and UN Middle East peace envoy Tor Wennesland said the "perpetrators must be brought to justice".

The European Union called for a "full, independent and transparent investigation".

The PA exercises limited powers over some 40 percent of the West Bank, occupied by Israel since the Six-Day War of 1967.

Israel, which controls all access to the territory and coordinates with the PA, directly administers the remaining 60 percent.