HEBRON, West Bank, June 24 (Reuters) - A Palestinian activist who died in the custody of President Mahmoud Abbas"s security forces on Thursday took blows to the head, a Palestinian rights group said after conducting an autopsy, adding the wounds indicated "an unnatural death". The family of Nizar Banat, a well-known critic of Abbas"s Palestinian Authority, said PA forces broke into his house in the occupied West Bank city of Hebron overnight and hit him repeatedly with a metal rod before arresting him. A PA spokesman could not immediately be reached for comment on the autopsy findings of the PA"s Independent Commission for Human Rights (ICHR). The PA had earlier declined to comment on the circumstances of Banat"s death. Earlier, hundreds of angry Palestinians marched towards Abbas"s presidential compound in Ramallah to demand he resign over Banat"s death, which drew calls by the United Nations, the U.S. State Department and the European Union for a transparent investigation. Prime Minister Mohammad Shtayyeh, an Abbas appointee, ordered the formation of an investigation committee into Banat"s death that he said would include the PA"s ICHR. But in a sign of public distrust with the PA inquiry, ICHR said it would lead its own investigation. ICHR conducted an autopsy with the family"s permission, and announced its initial findings on Thursday night. "The autopsy showed injuries represented by bruises and abrasians in many areas of the body, including the head, neck, shoulders, chest, back, and upper and lower extremities, with binding marks on the wrists and rib fractures," the ICHR said. "The preliminary autopsy results also indicate ... an unnatural death, but determining the principal cause of death, from a clinical point of view, requires waiting for laboratory results from tissue samples," it added in a statement. Palestinians renewed protests in central Ramallah later on Thursday. Some clashed with security forces who threw tear gas and stun grenades to disperse them. "NO ANOMALY" Banat, 43, was a social activist who had accused Abbas"s PA of corruption, including over a short-lived COVID-19 vaccine exchange with Israel this month and Abbas"s postponement of a long-delayed election in May. Banat had registered as a parliamentary candidate for that contest. Abbas regularly arrests his critics, human rights groups say, and has ruled the PA by decree for well over a decade. "The crushing death of activist Nizar al-Banat shortly after his arrest by the PA is no anomaly. PA security forces have for years systematically arbitrarily arrested, mistreated & tortured critics and dissidents," said Omar Shakir of Human Rights Watch. The PA rejects accusations it is corrupt and that it arrests people for their political views. It also denies torture. Hebron Governor Bakri said in a statement that Banat"s arrest was on the orders of the PA attorney-general. Banat"s family told Reuters that PA security forces broke into their house in the middle of the night, pulled Banat from his bed and started to beat him. "They hit him on his head with iron bars, which they had used to open the windows," Banat"s cousin, Hussein, 21, said. "They beat him continuously for eight minutes. If you came to arrest him, take him. Why the brutality?" "SHOCKED" The U.S. State Department said Washington was deeply disturbed by Banat"s death and called on the Palestinian Authority to conduct a thorough and transparent investigation. "We have serious concerns about Palestinian Authority restrictions on the exercise of freedom of expression by Palestinians and harassment of civil society activists and organizations," State Department spokesman Ned Price said in a statement. The United Nations Middle East peace envoy, Tor Wennesland, said on Twitter he was alarmed and saddened by the death, and also called for a transparent investigation. The European Union delegation to the Palestinians said on Twitter it was shocked and saddened, adding a "full, independent and transparent investigation should be conducted immediately." The PA exercises limited self-rule in the Israeli-occupied West Bank, home to 3.1 million Palestinians. On Monday, Banat, who had 100,000 Facebook followers, condemned PA officials as mercenaries over the COVID-19 vaccine exchange deal, which the PA swiftly cancelled. Banat planned to run for the Palestinian parliament on May 22. Abbas called off that election, citing Israeli controls over Palestinians in East Jerusalem. Opponents say Abbas cancelled the vote to avoid losing to Islamists, something he denies. read more