A Palestinian human rights activist died Thursday shortly after being arrested by Palestinian Authority (PA) security forces in the occupied West Bank, a provincial governor said.
His family reported that he was beaten to death.
Nizar Banat, 43, a PA critic from the flashpoint city of Hebron, was arrested in a dawn raid Thursday by Palestinian security forces, Hebron governor Jibrin al-Bakri said.
"Following... a summons from the public prosecution to arrest citizen Nizar Khalil Muhammad Banat, a force from the security services arrested him at dawn," Bakri said in a statement carried by the official WAFA news agency.
No reason was given for his arrest.
Banat's family accused security forces of "hitting him on the head with wooden sticks and bits of iron" and "deliberately murdering" him, they told the Palestinian news site Quds.
The governor said that during Banat's arrest, "his health deteriorated".
"He was immediately transferred to the Hebron government hospital... After he was examined by doctors, he was pronounced dead."
Banat was known for his videos posted on Facebook, in which he denounced alleged corruption in the PA.
He had registered as a candidate in the Palestinian parliamentary election which had been due to be held in May before president Mahmud Abbas postponed it indefinitely.
Bakri gave no indication of the cause of death, but both he and prime minister Mohammad Shtayyeh said an investigation had been launched.
Asked by AFP, Palestinian security forces declined to comment.
- EU 'shocked' -
Some 300 people gathered in Ramallah, the seat of the PA, calling for Abbas to quit.
"The arrests do not scare us," they chanted, brandishing portraits of Banat, an AFP journalist reported.
Islamist movement Hamas, which controls the Gaza Strip, said it held president Abbas "fully responsible for the repercussions" of Banat's death.
The European Union delegation to the Palestinians said it was "shocked and saddened" by Banat's death, adding that a "full, independent and transparent investigation should be conducted immediately".
The EU had voiced concern last November after Banat spent four days in custody in Jericho, and again expressed concern in May after Palestinian security forces raided Banat's home.
"Violence against politicians and human rights defenders is unacceptable," the EU's representative to the Palestinians said in May, calling for the PA to ensure the "respect for freedom of expression and the protection of human rights activists".
On Tuesday, another Hebron-based Palestinian human rights activist, Issa Amro, said he was briefly detained after posting criticism of political detentions on Facebook.
An opinion poll published earlier this month by the Palestinian Center for Policy and Survey Research found that 84 percent of Palestinians believe the PA is corrupt.
The PA exercises only 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, directly administers the remaining 60 percent.