Mr Abed described being kidnapped near his house by a group of five men who were armed with guns and machetes.
He was taken to a semi-demolished house, beaten, and called “an agent for Israel” and “a traitor”.
The leader of the group told Mr Abed’s assailants to break his fingers so he could not again write criticism of Hamas or “the heroic events of 7 October”.
After a group of passers-by attempted to intervene, the attackers fired shots into the air and told them to stay away, claiming they were from Hamas security forces.
Eventually, the assailants left and bystanders were able to take Mr Abed to a hospital.
Mr Abed is considered a popular figure. Before the war, had been arrested multiple times for speaking out against Hamas rule.
On Monday morning, Mr Abed wrote a long criticism of Hamas on Facebook, accusing the group of “dividing the Palestinian people” and “quashing their dream of a state”.
“We are tired, world,” he wrote, “we are really tired.”
Last week, in an interview with the BBC, he said: “[Hamas] has a lot of support among those outside Gaza’s border, who are sitting under air conditioners in their comfortable homes, who have not lost a child, a home, a future, a leg.”
Days earlier, he criticised Hamas in an interview with Saudi TV channel Al Arabiya. A clip from the interview was picked up on TikTok.
In 2019, Mr Abed helped organise protests over the state of Gaza’s economy.
Fatah, the ruling party in the West Bank and political rival of Hamas, released a statement on Monday condemning “the blatant assault on activist Amin Abed in Gaza”.
It did not name Hamas, but said the “de facto authorities in Gaza” had allowed “criminality” to spread in the enclave and held them fully responsible for Abed’s well-being.
Hamas violently ousted Fatah from the Gaza Strip in 2007, a year after winning national elections, reinforcing its power there and deepening a schism between the two dominant Palestinian groups.
Gaza’s Hamas-run police force has largely disappeared from the streets since the start of the war because of being targeted in Israeli air strikes, though the group remains the official authority in the territory.
The BBC has approached Hamas for comment.
The Israeli military launched a campaign in Gaza to destroy Hamas in response to its attack on southern Israel on 7 October, during which about 1,200 people were killed and 251 others were taken hostage.
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